Cover Well Construction Guide

1890’s

1950’s

1990’sEvolution of Well Construction in Ohio

State of Ohio

Technical Guidance for Well Constructionand

Ground Water Protection

by the

State Coordinating Committee on Ground Water2000

STATE OF OHIO

TECHNICAL GUIDANCE FOR WELL CONSTRUCTION ANDGROUND WATER PROTECTION

BY THE

STATE COORDINATING COMMITTEE ON GROUND WATER2000

ii

Table of Contents

Table of Contents .............................................................................................................................................................. iiList of Figures ................................................................................................................................................................... vList of Tables .................................................................................................................................................................... viPreface ............................................................................................................................................................................. viiAcknowledgements ........................................................................................................................................................ viiiIntroduction ...................................................................................................................................................................... 1

Purpose of the Guidance ........................................................................................................................................... 1Definitions ................................................................................................................................................................ 2Existing Regulations ................................................................................................................................................. 2

Siting Considerations ..................................................................................................................................................... 3Sanitary Isolation ................................................................................................................................................. 6Areas of Known Contamination .......................................................................................................................... 7Proximity to Surface Water .................................................................................................................................. 7Sole Source Aquifers and Wellhead Protection.................................................................................................... 8

Well Construction Materials and Equipment ................................................................................................................. 8Materials Used In The Drilling Process ............................................................................................................... 8Materials Used To Construct A Well .................................................................................................................... 9

Well Construction Procedures ..................................................................................................................................... 12General Procedures ............................................................................................................................................ 12Geological Considerations ................................................................................................................................. 16

Unconsolidated Formations ...................................................................................................................... 16Wells Developed in Consolidated Formations ......................................................................................... 18Wells Developed in Unconfined Aquifers ................................................................................................ 18Wells Developed in Confined Aquifers .................................................................................................... 19Wells Penetrating Multiple Aquifers ........................................................................................................ 20

Special Geologic Conditions .............................................................................................................................. 20Flowing Wells ........................................................................................................................................... 20Cavernous or Highly Fractured Formations ............................................................................................. 22Mine Shaft/Abandoned Mine Wells ......................................................................................................... 22Brine-Producing Formations .................................................................................................................... 26Gas-Producing Formations ....................................................................................................................... 26

Well Development Procedures..................................................................................................................................... 26Mechanical Techniques ...................................................................................................................................... 27Chemical Techniques ......................................................................................................................................... 29

Well Testing ................................................................................................................................................................. 29Testing For Quantity .......................................................................................................................................... 29Guidelines For Quantity Testing Requirements ................................................................................................. 30Testing For Quality ............................................................................................................................................ 32Chemical sampling ............................................................................................................................................. 33

Well Completion .......................................................................................................................................................... 33Well Disinfection ......................................................................................................................................................... 35Well Maintenance ........................................................................................................................................................ 36Well Alterations ........................................................................................................................................................... 37

Reporting Requirements .................................................................................................................................... 38Temporary Wells and Other Types of Subsurface Installations ................................................................................... 38

Dewatering Wells ............................................................................................................................................... 39Test Borings ....................................................................................................................................................... 39Geothermal Wells ............................................................................................................................................... 39Cathodic Protection and Ground Wells .............................................................................................................. 39Elevator Shafts ................................................................................................................................................... 39

Conclusions.................................................................................................................................................................. 39References........................................................................................................................................................................ 41

iii

Table of Contents continued

Listing of American Society for Testing and Materials (ASTM) Standards Referenced ............................................ 44Listing of American Petroleum Institute (API) Standards Referenced ....................................................................... 44Listing of National Sanitation Foundation (NSF) Standards Referenced ................................................................... 44Listing of Water Systems Council Standards Referenced ........................................................................................... 44

Glossary ........................................................................................................................................................................... 45Appendix I Well Drilling Methods Used in Ohio ......................................................................................................... 48Appendix II Grouting Materials ................................................................................................................................... 50

Cement-Based Grouts .................................................................................................................................................. 50Cement Properties .............................................................................................................................................. 50Cement Types ..................................................................................................................................................... 50Neat Cement Grout ............................................................................................................................................ 52Concrete Grout ................................................................................................................................................... 52Other Cement Additives ..................................................................................................................................... 53

Bentonite-Based Grouts ............................................................................................................................................... 53Clay Properties ................................................................................................................................................... 53Properties of Bentonite/Water Slurries ............................................................................................................... 53High-Solids Bentonite Grout ............................................................................................................................. 54Powdered Bentonite/Clay Grout ........................................................................................................................ 54Granular Bentonite ............................................................................................................................................. 55Coarse Grade Bentonite ..................................................................................................................................... 55Pelletized Bentonite ........................................................................................................................................... 55

Appendix III Well Quantity Testing ............................................................................................................................. 58Quantity Testing Methodology .................................................................................................................................... 58

Electrical tape method ........................................................................................................................................ 58Wetted tape method ............................................................................................................................................ 58Airline method ................................................................................................................................................... 58

Flow Rate Measurement .............................................................................................................................................. 59Circular orifice weir ........................................................................................................................................... 59Commercial water meters .................................................................................................................................. 59Container/timed method ..................................................................................................................................... 60Weirs and flumes ................................................................................................................................................ 60

Simple Tests To Estimate Well Yield ........................................................................................................................... 60Bailing test method ............................................................................................................................................ 60Air blow test method .......................................................................................................................................... 61Air lift test method ............................................................................................................................................. 61Variable pumping rate method ........................................................................................................................... 61

Pumping Test To Evaluate Well Performance ............................................................................................................. 61Step-drawdown tests .......................................................................................................................................... 61Constant rate tests .............................................................................................................................................. 62

Preparation ................................................................................................................................................ 62Test Rate ................................................................................................................................................... 62Test Duration ............................................................................................................................................ 62Recovery Data .......................................................................................................................................... 62Pumping Tests To Evaluate Aquifer Characteristics ................................................................................ 62Data Collection And Record Keeping ...................................................................................................... 63

Appendix IV Water Sample Collection......................................................................................................................... 65Coliform bacteria sampling ......................................................................................................................................... 65

Appendix V Well Disinfection........................................................................................................................................ 67Disinfection of a Drilled Well ...................................................................................................................................... 67Calculation and Examples ........................................................................................................................................... 67

Disinfection of a Dug or Bored Well ................................................................................................................. 68 Appendix VI Monitoring Well Design and Installation ............................................................................................. 70

Design of Multiple-Interval Systems ........................................................................................................................... 70Well Clusters............................................................................................................................................. 70

iv

Table of Contents continuedMulti-Level Wells .............................................................................................................................................. 70Nested Wells ....................................................................................................................................................... 71Single Riser/Flow-Through Wells ...................................................................................................................... 71Casing ................................................................................................................................................................. 71

Casing Types............................................................................................................................................. 71Fluoropolymers ................................................................................................................................ 71Metallics ........................................................................................................................................... 72Thermoplastics ................................................................................................................................. 72

Type Selection .......................................................................................................................................... 73Hybrid Wells ...................................................................................................................................................... 73Coupling Mechanisms ........................................................................................................................................ 74

Diameter ................................................................................................................................................... 74Installation ................................................................................................................................................................... 75

Intakes ................................................................................................................................................................ 75Filter Pack .......................................................................................................................................................... 75

Types of Filter Packs ................................................................................................................................ 75Nature of Artificial Filter Pack Material .................................................................................................. 75Dimension of Artificial Filter Pack .......................................................................................................... 76Artificial Filter Pack Installation .............................................................................................................. 77

Screen .......................................................................................................................................................................... 78Screen Types ...................................................................................................................................................... 78Slot Size ............................................................................................................................................................. 78Length ................................................................................................................................................................ 78Open Borehole Intakes ....................................................................................................................................... 79

Annular Seals ............................................................................................................................................................... 79Materials ............................................................................................................................................................. 80

Neat Cement Grout ................................................................................................................................... 80Bentonite................................................................................................................................................... 81

Seal Design .................................................................................................................................................................. 81Seal Installation .................................................................................................................................................. 81Surface Seal/Protective Casing Completions ..................................................................................................... 82

Surface Seal .............................................................................................................................................. 82Above-Ground Completions .................................................................................................................... 82Flush-to-Ground Completions .................................................................................................................. 82

Documentation ............................................................................................................................................................. 83Maintenance ................................................................................................................................................................. 84

Appendix VII Contact Agencies .................................................................................................................................... 85

v

List of Figures

Figure 1. Example of a completed well log and drilling report. ......................................................................................... 4Figure 2. Example of a completed well sealing report. ...................................................................................................... 5Figure 3. Examples of recommended well construction using cable tool drilling methods. ............................................ 14Figure 4a. Example of recommended rotary-drilled well construction for wells developed in unconsolidated forma-

tions–total annular space 2 inches or more. .............................................................................................................. 15Figure 4b. Example of recommended rotary-drilled well construction for wells developed in consolidated formations–

total annular space 4 inches or more. ........................................................................................................................ 15Figure 5. Example of well construction using hollow stem augers. (Modified from Hackett, 1987 and 1988) .............. 16Figure 6. Example of recommended driven well construction. ........................................................................................ 16Figure 7. Grouting the annular space of wells with coarse grade bentonite products using the pouring method. (Modi-

fied from Wisconsin Department of Natural Resources, 1993) ................................................................................ 18Figure 8. Confined and unconfined aquifers. (After U.S. Department of Interior, 1997) ................................................ 19Figure 9a. Recommended well construction for wells penetrating multiple unconsolidated aquifers. ............................ 21Figure 10a. Rotary method for flowing well construction-confined bedrock aquifer with an unconsolidated confining

bed. ............................................................................................................................................................................ 22Figure 10b. Cable tool method for flowing well construction-confined bedrock aquifer with an unconsolidated confin-

ing bed. ...................................................................................................................................................................... 22Figure 11a. Rotary method for flowing well construction where both confining bed and aquifer are unconsolidated-

double casing construction. ....................................................................................................................................... 25Figure 11a. Cable tool method for flowing well construction-confined unconsolidated aquifer with an unconsolidated

confining bed. ............................................................................................................................................................ 25Figure 12. Recommended grouting procedures for wells penetrating fractured or cavernous formations. ..................... 25Figure 13. Recommended grouting procedures for wells penetrating fractured or cavernous formations where an upper

fractured or cavernous zone has been sealed off. ...................................................................................................... 25Figure 14. Example of pitless adapter installation. .......................................................................................................... 33

Appendix III Well Quantity Testing ............................................................................................................................. 58Figure 1. Example of airline setup and operation. ............................................................................................................ 59Figure 2. Detail of orifice weir construction. ................................................................................................................... 61

Appendix VI Monitoring Well Design and Installation ............................................................................................. 70Figure 1. Cross-section of a typical single-riser/limited interval monitoring well. .......................................................... 70Figure 2. Artificial filter pack design criteria (Source: Design and Installation of Ground Water Monitoring Wells by

D.M. Nielsen and R. Schalla, Practical Handbook of Ground Water Monitoring, edited by David M. Nielsen,Copyright 1991 by Lewis Publishers, an imprint of CRC Press, Boca Raton, Florida. With permission.) .............. 77

Figure 3. Selection of screen slot size based on the filter pack grain size. (Source: Design and Installation of GroundWater Monitoring Wells by D.M. Nielsen and R. Schalla, Practical Handbook of Ground Water Monitoring, editedby David M. Nielsen, Copyright 1991 by Lewis Publishers, an imprint of CRC Press, Boca Raton, Florida. Withpermission.) ............................................................................................................................................................... 79

Figure 4. Tremie pipe emplacement of annular seal material. (Source: Design and Installation of Ground Water Moni-toring Wells by D.M. Nielsen and R. Schalla, Practical Handbook of Ground Water Monitoring, edited by DavidM. Nielsen, Copyright 1991 by Lewis Publishers Division, an imprint of CRC pressPress, Boca Raton, Florida.With permission.) ...................................................................................................................................................... 82

Figure 5. Typical flush-to-ground monitoring well completion.(Source: Design and Installation of Ground Water MonitoringWells by D.M. Nielsen and R. Schalla, PracticalHandbook of Ground Water Monitoring, edited by David M. Nielsen, Copyright 1991 by Lewis PublishersDivision, an imprint of CRC Press, Boca Raton, Florida. With permission.) ........................................................... 83

vi

List of Tables

Table 1. Common Uses for Water Wells ............................................................................................................................. 3Table 2. Well Use Classification ....................................................................................................................................... 31Table 3. Volume of Water in Well ..................................................................................................................................... 37Table 4. Amount of Chlorine Added to 100 Gallons of Water for Disinfection ............................................................... 37

Appendix II Grouting Materials ................................................................................................................................... 53Table 1. Grout Properties .................................................................................................................................................. 51Table 2. Permeability of Various Sealing Materials ......................................................................................................... 51Table 3. Cement Curing Time Required ........................................................................................................................... 51Table 4. Grout Slurry Densities ........................................................................................................................................ 55

Appendix III Well Quantity Testing .................................................................................................................................Table 1. Estimating Water Usage...................................................................................................................................... 64

Appendix V Well Disinfection.......................................................................................................................................... 7Table 1. Volume of Water in Well ..................................................................................................................................... 67Table 2. Amount of Chlorine Added to 100 Gallons of Water for Disinfection ............................................................... 67Table 3. Quantity of Bleach for a Bored or Dug Well (1000 ppm) .................................................................................. 68

Appendix VI Monitoring Well Design and Installation ............................................................................................. 73Table 1. Common filter pack characteristics for typical screen slot sizes. (From Nielsen and Schalla, 1991) ................ 77Table 2. ASTM Cement Designation (modified from Gaber and Fisher, 1988) ............................................................. 80

vii

Preface

In early 1992, the State Coordinating Committee on Ground Water identified a list of major issuesand problems that they determined should be addressed in some form by the Committee. The lack ofconsistent standards and regulations regarding the construction of wells and test borings was identi-fied as a major issue of concern by the Committee. This issue was also raised during discussionsbetween the drilling industry, represented by the Ohio Water Well Association and the Private WaterSystems Workgroup, which formed to address issues related to private water systems. The Ohio WaterWell Assocation also identified the need for consistent well construction standards across state agencyprograms and the need for regulation of nonpotable wells. Due to increasing concerns by many of theparticipating state agencies and the well drilling industry, the widespread acceptance of the TechnicalGuidance Document for Sealing Unused Wells published in May, 1996, and efforts by the OhioDepartment of Health to implement improvements in the private water systems program, the Commit-tee decided to form a subgroup in June, 1996 to develop consistent technical standards for the con-struction of wells and test borings. Both the Ohio Environmental Protection Agency and the OhioDepartment of Health have committed to revising their rules regarding well construction to be consis-tent with the resulting new technical guidance document. The Well Construction Workgroup beganmeeting in July, 1996; what follows is the product of months of meetings, research, edits, and revi-sions.

Throughout this document are references to proprietary materials or products. These referencesshould in no way be interpreted as endorsements for any particular brand name or manufacturer, andare used only for illustrative or comparative purposes.

This guidance does not apply to wells constructed for the purpose of injecting fluids into thesubsurface (except as it may augment, not supersede, rule requirements). The authority over injectionwells depends on the well classification. For more information contact the Ohio EnvironmentalProtection Agency, Division of Drinking and Ground Waters, Underground Injection Control Unit.

viii

Acknowledgements

The preparation of the State of Ohio Technical Guidance for Well Construction and Ground WaterProtection involved the contribution and hard work of a number of individuals on the Well Construc-tion Standards Workgroup of the State Coordinating Committee on Ground Water. The developmentof this technical guidance was supported by the state agencies participating on the Committee. Grate-ful thanks and acknowledgement is given to the committee members who dedicated many hours inworkgroup meetings, and their time, expertise, and assistance in authoring and reviewing this docu-ment. The workgroup would also like to thank the many industry professionals who took the time toparticipate in the meetings, or to review and provide comments on this document. Special apprecia-tion and acknowledgement is given to Katherine Sprowls for her work on organizing and editing thisguidance, and to David Orr for his work and assistance on preparing the figures, desktop publishing,and printing of this document.

Well Construction Workgroup MembersFederal, State, and Local Agency Representatives

Rebecca Petty* (workgroup chair) Division of Water, Ohio Department of Natural Resources/OhioDepartment of Health

Katherine Sprowls* (editor) Division of Water, Ohio Department of Natural Resources

John Arduini Division of Drinking and Ground Waters, Ohio Environmental Protec-tion Agency

Judy Hamill Division of Drinking and Ground Waters, Ohio Environmental Protec-tion Agency

Ashley Bird Division of Drinking and Ground Waters, Ohio Environmental Protec-tion Agency

Charles Martin* Division of Drinking and Ground Waters, Ohio Environmental Protec-tion Agency

Rich Bendula* Division of Drinking and Ground Waters, Ohio Environmental Protec-tion Agency

Robert Van Horn Division of Geological Survey, Ohio Department of Natural Resources

Scott Golden Bureau of Local Services, Ohio Department of Health

Russell Smith* Bureau of Local Services, Ohio Department of Health

John Wells* Bureau of Local Services, Ohio Department of Health

Kevin Hodnett Bureau of Underground Storage Tank Regulation, State Fire Marshal

Jack Tomei Akron Health Department, representing the Ohio Public HealthAssociation

Brian Benick* Medina County Health District, representing the Ohio EnvironmentalHealth Association

Martin Baier Cuyahoga County Health District

Tim Horgan* Cuyahoga County Health District, representing the Association ofOhio Health Commissioners

Joe Ebel Morrow County Health District

Larry Berger Ohio Department of Agriculture

Jeff DeRoche United States Geological Survey, Water Resources Division

Greg Nalley United States Geological Survey, Water Resources Division

Peter Wright United States Geological Survey, Water Resources Division

ix

Industry RepresentativesWalt Sandefur* Sprowls Drilling, representing the Ohio Water Well Association

David Yeager* Yeager Drilling

Paul Kotterman* Kotterman Well Drilling

Hewitt Fredebaugh Fredebaugh Well Drilling

Fred Schreiber Fred’s Water Service

Vernon Widows Reynolds, Inc.

Steve Wright Frontz Drilling

Mike Caprioni Jersey West Drilling Company

Bill Curry Curry Drilling

Jeff Hardman Hardman Drilling

Edward Schlaack Layne–Ohio, Inc.

Alan Belasco Belasco Drilling

Supplier RepresentativesMike Piche* Cook Screens, Inc.

Don Baron U.S. Filter/Johnson Screens

Zeke Zdenek Cook Screens, Inc.

ConsultantsHerb Eagon* Eagon and Associates, Inc.

Linda Aller Bennett and Williams Environmental Consultants, Inc.

Joan Brasaemle Environmental Mitigation Group

*Denotes text authorship or contribution to the text

State Coordinating Committee on Ground Water Member AgenciesOhio Environmental Protection Agency

Ohio Department of Natural Resources

Ohio Department of Health

Ohio Department of Agriculture

Public Utilities Commission of Ohio

Ohio Department of Commerce - State Fire Marshal

Ohio Department of Development

Ohio Department of Transportation

United States Geological Survey

Natural Resource Conservation Service

–Rebecca Petty

1

Introduction

The state of Ohio currently estimates that over 1 million potable and non-potable water wells and testborings have been drilled statewide. Records regarding the construction and location of these wells arefiled with the Ohio Department of Natural Resources (ODNR), Division of Water. Based on the well logfiling data, approximately 80% of these wells are used for drinking water and are regulated under thePrivate Water Systems Program at the Bureau of Local Services, Ohio Department of Health (ODH), orthe Public Water Supply Program regulated by the Division of Drinking and Ground Waters, Ohio Envi-ronmental Protection Agency (OEPA). The remaining 20% of the well logs filed each year represent wellsdrilled for non-potable water supply. Currently, there are no regulations for well construction or sealing ofunused non-potable wells.

State agencies in conjunction with private industry associations have developed several strategies andwater plans that identify the need to establish statewide consistent construction standards for water wells.The Ohio Ground Water Protection and Management Strategy (1985) and Ohio’s Water, Ohio’s Future(1994) both identify the need to establish consistent well construction and well sealing standards and toimplement those standards through subsequent changes in the Ohio Revised or Administrative Code at therespective state agencies. In 1993, the State Coordinating Committee on Ground Water (SCCGW), identi-fied the need for consistent water well and test boring construction and sealing regulations as one of thetop priority issues to be addressed by the committee. The SCCGW developed specific recommendationsregarding this issue which was forwarded to the state agency directors. As a result of these recommenda-tions, a workgroup of the SCCGW formed to develop the State of Ohio Technical Guidance for SealingUnused Wells (1996). The Private Water Systems Workgroup was formed in early 1995 to develop a planto address increasing concerns regarding private water systems and non-potable wells. As a result of thisworkgroup’s efforts, both the drilling industry and public health officials identified the need for consistentwell construction standards to be developed concurrent with changes in the regulatory programs. The WellConstruction Standards Workgroup was formed to identify and develop the following standards andtechnical information contained in this document.

Purpose of the GuidanceThe primary purpose of this guidance is to provide consistent state standards on proper well siting,

construction, testing, and development/rehabilitation to ensure the protection of public health and thestate’s ground water resources. A poorly constructed well can provide a direct path for contaminants at thesurface to migrate into the ground water. The application of consistent statewide standards by the drillingindustry and the state regulatory programs, together with the proper education and support of the indi-vidual well owner, is critical to ensure the protection of the ground water resources for drinking water andother beneficial uses. Standards also help ensure that the well provides a reliable, adequate water supplyfor a reasonable cost, and that long-term maintenance costs are minimized. These factors become particu-larly important when evaluations are made regarding the economic feasibility of rural water lines andcustomer satisfaction with existing ground water supplies from individual wells.

The guidance is designed to be used by drilling contractors, hydrogeologists, engineers, and state andlocal regulatory officials for siting, constructing and developing water wells. Information on aquifercharacteristics and ground water availability should be obtained prior to the design, drilling and develop-ment of the well. This information should include the aquifer lithology and thickness, depth and estimatedyield, and thickness and characteristics of the vadose zone or shallow aquifers that will be penetrated. Thedesign of the water system should also consider the maximum and peak yields required by the user orhousehold on a daily and long-term basis. The drilling contractor, homeowner, and local or state regula-tory official need to work closely together to design a water supply system that is safe, provides themaximum yield required for the intended use, and minimizes maintenance requirements while ensuringthe long-term reliability of the well.

This guidance describes minimum construction standards for both permanent and temporary wellinstallations. The guidance should be applied to all types of wells used to withdraw ground water regard-less of purpose. The guidance includes a discussion of the materials used for well drilling and construc-tion, general construction standards, and specific construction requirements under unique hydrogeologicconditions found in Ohio. The intent of this guidance is to provide a set of uniform standards combinedwith basic information regarding the application of the standard for well construction materials andconstruction methods. However, other regulatory authorities may have additional requirements not dis-

2

cussed in this document that are specific to their respective programs. It is the drilling contractor/welldesigner’s responsibility to ensure that all regulatory statutes and requirements are met before the well isconstructed. This document is not designed to be a comprehensive guide on well drilling and constructionmethods. Information regarding well drilling methods has been included in this document for reference.Additional references describing drilling methods and materials can be found in Appendices I and II. Thisguidance also includes standards and procedures for constructing monitoring wells which are addressed inAppendix VI.

Recommendations in this document are indented, italicized, and enclosed by lines. Each recommenda-tion or set of recommendations is followed by additional explanatory text.

Although proper well construction is necessary to ensure the protection of ground water resources, it isequally important that any abandoned well, properly constructed or not, be properly sealed to preventfuture contamination. A companion document to this guidance has been developed that provides guidancefor sealing unused wells. The State of Ohio Technical Guidance for Sealing Unused Wells (1996) de-scribes the recommended procedures, practices and materials for sealing wells that have been abandonedor are no longer used.

DefinitionsA consistent set of definitions for common terms was developed for use throughout this document to

facilitate the discussion and application of the construction standards. These definitions may also be usedby the regulatory agencies to help ensure uniformity in the interpretation and application of these stan-dards across the state. Several commonly used terms are defined in the following paragraphs to help thereader clearly understand the purpose and scope of this document. Additional definitions of terms high-lighted in bold throughout the document can be found in the glossary.

Ground water is defined as any water below the surface of the earth in a zone of saturation.Aquifer means a consolidated or unconsolidated geologic formation or series of formations that is

capable of receiving, storing, or transmitting water to wells or springs.Well is defined as any excavation, regardless of design or method of construction, created for any of

the following purposes: 1) removing ground water from or recharging water into an aquifer, excludingsubsurface drainage systems installed to enhance agricultural crop production or urban or suburbanlandscape management or to control seepage in dams, dikes or levees; 2) determining the quantity, quality,level, or movement of ground water in, or the stratigraphy of, an aquifer; and 3) removing or exchangingheat from ground water, excluding horizontal trenches that are installed for water source heat pumpsystems.

Temporary well installation is a boring or well that is to be installed and used for less than one year.Any well installed for a period of greater than one year should be considered a permanent installation andshould follow the guidelines described in this document

Water wells are installed for a wide variety of uses. Table 1 lists common uses and types of wells. Thisguidance should be applied to all of the wells listed in Table 1. There are a number of special types ofwells or excavations that are regulated under federal and/or state laws. These types of wells include ClassIV and V injection wells and monitoring or remediation wells regulated by the Ohio EnvironmentalProtection Agency. Wells used for storm water or surface water drainage are considered Class V injectionwells and have separate permitting and design requirements not covered under this document.

Other types of wells that may be widely installed across the state include elevator shafts, foundation ortest bores, direct push bores, cathodic protection wells, seismic monitoring wells, and radial collectorwells. Although this guidance does not specifically cover construction standards for these types of wells orexcavations, many of the standards included herein can be directly applied to the installation of thesestructures. Any type of boring or vertical installation into the subsurface that penetrates one or moreaquifers should use the recommended materials and procedures for drilling and completing the well,installation, or borehole to ensure the protection of ground water quality and prevent the diminution ofground water quantity.

Existing RegulationsA variety of state agencies regulate the construction of water wells and borings in Ohio depending on

the use of water and/or the purpose of the well. Water wells used for public water supplies are regulated by

3

the Ohio Environmental Protection Agency (EPA) under the Ohio Revised Code Section 6109. Publicwater supplies can be further categorized into community water systems, transient non-community watersystems, and non-transient non-community water systems. Definitions and construction regulations forthese systems are described in the Ohio Administrative Code Chapter 3745. Public water systems aredefined as a system for the provision to the public of piped water for human consumption, if such systemhas at least fifteen service connections or regularly serves an average of at least twenty-five individualsdaily at least sixty days out of the year. Well site acceptance must be granted by the Ohio EPA prior todrilling a potable water well for use by a public water system. Detailed construction plans for the well,treatment, and distribution systems must be approved by the director of the Ohio EPA prior to placing thewell and/or water system in service.

Private water systems are regulated by the Ohio Department of Health under the Ohio RevisedCode Section 3701. This program is administered through the local health departments and applies toany well, spring, cistern, pond or hauled water and any equipment for the collection, transportation,filtration, disinfection, treatment or storage of such water extending from and including the source ofthe water to the point of discharge from a pressure tank or other storage vessel. A private watersystem is any water system for the provision of water for human consumption, if such system hasfewer than fifteen service connections and does not regularly serve an average of at least twenty-fiveindividuals daily at least sixty days out of the year. Rules regarding the materials, construction,treatment, rehabilitation, and sealing of private water systems are described in the Ohio Administra-tive Code Chapter 3701-28. Permits for private water systems are obtained from the local healthdepartment who conducts the siting and approval for the well.

Well log and sealing reports are required to be filed with the Division of Water, Ohio Department ofNatural Resources for any well as defined under the Ohio Revised Code Section 1521.05. Any person thatparticipates in the construction or sealing of a well is required to keep an accurate record and provide thatinformation on well log or sealing forms provided by the Division of Water. An example of a well logform and sealing report is shown in Figures 1 and 2, respectively. Definitions, requirements for filing andpenalties are also described under ORC Section 1521.05.

Other types of wells that are currently regulated also include any monitoring or remediation wellsrequired as part of any regulated facilities or activities under the CERCLA or RCRA program under theauthority of the Ohio EPA or the United States Environmental Protection Agency, or under the VoluntaryAction Program regulated by the Ohio EPA. Construction standards for monitoring wells have beendeveloped by the Ohio EPA and are included as Appendix VI. A listing of state agencies and contacts withregulatory authority related to well construction and ground water is included in Appendix VII.

Siting ConsiderationsThis section is intended to provide guidance on the siting of a new well to ensure that the well will

meet all applicable regulatory requirements for the setback of new wells from potential sources of con-tamination. These isolation standards vary, depending upon the intended use of the well. All potable wellsneed to get site acceptance from the appropriate agency prior to drilling a well. However, for all types ofwells it is important to select a location which minimizes the potential for contamination. A new well

Public Water SupplyPrivate Water SupplyAgricultural (Livestock Watering, Dairy)Irrigation/ChemigationOpen-loop Geothermal/ Closed Loop Vertical GeothermalIndustrial/Process WaterPower SupplyCoolingFire ProtectionDust ControlDewateringPressure ReliefRemediation (Recovery, Extraction, Interception, Air Sparging, Vacuum Extraction)

Table 1. Common Uses for Water Wells

4

WELL LOG AND DRILLING REPORTOhio Department of Natural Resources

Divison of Water, 1939 Fountain Square DriveColumbus, Ohio 43224-9971 Voice (614) 265-6739 Fax (614) 447-9503

TYPE OR USE PENSELF TRANSCRIBING

PRESS HARD

CONSTRUCTION DETAILS

Type of pump Capacity gpm

INDICATE DEPTH(S) AT WHICH WATER IS ENCOUNTERED. Show color, texture, hardness, and formation: sandstone, shale, limestone, gravel, clay, sand, etc. From

Completion of this form is required by section 1521.05, Ohio Revised Code - file within 30 days after completion of drilling.ORIGINAL COPY TO - ODNR, DIVISION OF WATER, 1939 FOUNTAIN SQ. DRIVE, COLS., OHIO 43224-9971

Blue - Customer's copy Pink - Driller's copy Green - Local Health Dept. copy

Drilling Firm

Address

Signed

Rotary

I hereby certify the information given is accurate and correct to the best of my knowledge.

DNR 7802.96

East

Sketch a map showing distance well lies from numbered state highways, streetintersections, county roads, buildings or other notable landmarks. If latitude andlongitude are available please include here:

WELL LOCATION

WELL TEST*

PUMP/PITLESS

Cable Augered Driven Other

SCREEN

GRAVEL PACK

GROUT

Borehole Diameter

Casing Diameter

Depth ft.inches

Length ft.in. in.Thickness

Borehole Diameter

Casing Diameter

Depth ft.inches

Length ft.in. in.Thickness

1

2

Casing Height Above Ground ft.

Type

Joints

Steel Galv. PVCOther

1

2

1

2

1

2

1

2

Threaded Welded SolventOther

1

2

1

2

1

2

1

2

(Filter Pack)

Material/Size Volume/Weight Used

Method of Installation

Depth: Placed FROM ft. TO ft.

Material

Method of Installation

Depth: Placed FROM ft. TO ft.

DRILLING LOG*

To

ODH Registration Number

City, State, Zip

Volume/Weight Used

Location of Well in State Planecoordinates, if available:

Source of Coordinates: GPS Survey Other

Y

.X +/- ft. or mN

S

Datum Plain: NAD27 NAD83

+/- ft. or m.. +/- ft. or m

Top of Casing Ground Level Other

Pre-Pumping Static Level ft.

Measured from:

Test Rate

Air Bailing OtherPumping*

gpm Duration of Test hrs.

Feet of Drawdown

Date

ft.*(Attach a copy of the pumping test record, per section 1521.05, ORC)

Quality

Lat: Long:

YesYes NoIs Copy Attached? Flowing Well?

Owner/Builder(Circle One or Both)

County

Address ofWell Location

Pump set at ft.

Pump installed by

South

West

North

Township

First Last

Number Street Name

City Zip Code +4

Permit No. Section/Lot No.(Circle One or Both)

Use of Well

Elevation of Well

Pitless Type

Sustainable Yield gpm

Elevation Source

*(If more space is needed to complete drilling log, use next consecutively numbered form.)

ft.Date of Well Completion Total Depth of Well

No

Date

BOREHOLE/CASING (measured from ground surface)

Slot SizeDiameter

ft. andSet Between ft.

ft.Screen Length

Type Material

xxxx

Delaware Trenton

E. J. Fudd

181 Green Cook Rd.

Sunbury 43074-9761960.95 20

Residential

195339 425 20 1922944 533 20

1084 5

Topo map

xx

40 12'09" 82 46'35"

20 12/10/95x

x 35 1

20 25

x x

Clear, 1ppm Fe, 30 gpg hardness, pH 7

Submersible 10 65 Adapter

Acme Drilling Co.

Acme Drilling Co. 1234 Main St.

Anytown, Ohio 56789

1/23/961111 12/10/95 127

Brown clay 0 15

Gray sandy clay 15 20

Sand & gravel (dry) 20 22

Gray clay w/gravel 22 33

Sand & gravel (dry) 33 39

Gray clay 39 119

Coarse sand & gravel 119 127

Water encountered at 122'

x

x 7 7/8 127 5 20 .327

5 102 .2651

Benseal/EZ Mud 175 gal

Pumped through 1" tremie tube118 surface

5 in .050 in 5Machine-slotted PVC

122 127

#4 Parry sand 400 lbs

Gravity pour 118 127

x

Figure 1. Example of a completed well log and drilling report.

5

PRESSURE GROUT - Pumped through 1" tremie tube.

East

Delaware Trenton 20

181 Green Cook Rd.

.2 South

Green Cook Rd.

E. J. Fudd

ACME DRILLING COMPANY 11111234 MAIN ST.Anytown, OH, 56789

12/22/95WELL NO LONGER NEEDED.

GOOD

Sunbury 43074-9761St. Rt. 37

1 9 5 3 3 9

X

20 1 9 2 2 9 4 44 3 20X

1 0 8 4 5

X

N/A

5 3

127 ft.5 in.Good

20 ft.127 ft.

12/22/95

127 surface Benseal/EZ Mud Slurry 130 gallons

LOCATION

County Township Section/Lot NumberOwner/Builder

Address of Well Location

City Zip Code +4

ORIGINAL WELL ODNR Well Log Number Copy attached? Yes or No

MEASURED CONSTRUCTION DETAILS Date of measurements

Depth of Well Static Water LevelSize of Casing Length of casingWell Condition

SEALING PROCEDUREMethod of Placement

Placement: From ToFrom ToFrom To

Was Casing Removed? Yes or No

Condition of CasingPerforations: From To

From To

Date Sealing PerformedReason(s) for Sealing

CONTRACTORName ODH Registration #AddressCity/State/Zip

Signature

WATER WELL SEALING REPORTOHIO DEPARTMENT OF NATURAL RESOURCES

Division of Water1939 Fountain Square Drive

Columbus, Ohio 43224-9971Voice: (614) 265-6739 Fax: (614) 447-9503

DNR 7810.96

Completion of this form is required by section 1521.05 (B) (9), Ohio Revised Code - file within 30 days after completion of sealing.ORIGINAL COPY TO - ODNR, DIVISION OF WATER, 1939 FOUNTAIN SQ. DRIVE, COLS., OHIO 43224

Blue - Customer's copy Pink - Driller's copy Green - Local Health Dept. copy

I hereby certify the information given is accurate and correct to the best of my knowledge.

Number Street Name

n, e, s, w road name

Circle One or Both

Circle One or Both

Property LocationDescription

n, e, s, w nearest intersectionmiles of

side ofon the

(circle one)

N

S .X Y+/-ft. or mLocation of Well in State Plane

coordinates, if available

Elevation of Well Datum Plain: NAD27 NAD83

Source of Coordinates: GPS Survey Other

. +/-ft. or m

. +/-ft. or m

Sealing Material Volume

(circle one)

Figure 2. Example of a completed well sealing report.

6

should be located only where the new well and its surroundings can be maintained in a sanitary condition,and only where surface and subsurface conditions will not allow contaminants to be conducted into thewell. In some cases it may not be possible to obtain a safe ground water supply due to extensive contami-nation in the area. In these areas an alternate water supply should be developed.

When evaluating a site for drilling a new well it is very important to consider past and future land usein the area. It is recommended that a limited hydrogeologic investigation be conducted in the area of thepotential well site prior to purchasing the property to determine if adequate water supplies are availableand if any water quality problems exist. It may also be beneficial to determine if any zoning is available toassist in protecting the future water supplies from potential sources of contamination. For new propertydevelopment, it is strongly recommended that the location of the water well be given priority over thelocation of the septic system. The owner and driller should work closely with the local health departmentor Ohio EPA district office to see if there are any specific contamination problems present in the area ofinterest before the well is drilled. In cases where a new well is drilled as a replacement for a well that hasfailed or become contaminated, it is important that the old well be properly sealed to prevent ground watercontamination from the surface or any contaminated zones. In cases where the new well is an addition toan existing ground water supply, the wells should be spaced to minimize any interference effects.

Sanitary IsolationA water well should be located only where the well and its surroundings can be maintained in a sani-

tary condition, and only where surface and subsurface conditions will not permit contamination of the wellor aquifer.

Recommended minimum distances (except for public supply wells) between a water sourceand common potential sources of contamination are:

Sewers and drains constructed with watertight pipe......................................... 10 feetUnderground fuel oil tanks, gasoline storage tanks,LP tanks, chemical tanks ................................................................................... 50 feetSewage tanks and adsorption fields ................................................................. 50 feetLeaching pit and leaching privies ...................................................................... 100 feetVault privies ....................................................................................................... 50 feetStables, manure piles, etc. ................................................................................ 50 feetStreams, lakes, ponds, ditches, roads, etc. ...................................................... 25 feetProperly sealed well .......................................................................................... 10 feetExisting properly constructed water well* ......................................................... 10 feetStructures .......................................................................................................... 10 feetAbove-ground chemical storage tanks w/secondary containment ................... 10 feetAbove-ground chemical storage tanks w/o secondary containment ................ 25 feetVertical or horizontal geothermal loop systems w/lowtoxicity heat transfer fluid .................................................................................. 25 feetVertical or horizontal geothermal loop systems w/hightoxicity heat transfer fluid .................................................................................. 50 feet

*If existing well construction is unknown or of poor quality, then the well should be properlysealed.

For all public water supply wells, the new well shall be located at such distances from known orpossible sources of contamination as the Director determines are necessary to safeguard the health ofpersons using water from the well, and to prevent contaminants from entering ground water (OAC 3745-9-04(C)(1)).

The isolation standards for public water supply wells are based upon the estimated waterusage of the system and are listed below as a minimum distance from potential sources ofcontamination:

7

Estimated Water Usage (Q) Minimum Isolation Radius0-2,500 gallons per day (g.p.d.) ___________________ 50 feet

2,501-10,000 g.p.d. ____________________________ Square root of Q

10,001-50,000 g.p.d. ___________________________ 50 + Q/200

Over 50,000 g.p.d. _____________________________ 300 feet

All of the isolation recommendations discussed previously are minimums only. They are subject tochange based on actual site conditions. It may be necessary to increase isolation distances to minimize thepotential for contamination where fractured bedrock or sand and gravel aquifers are near the surface andlack natural protection from contamination. In areas where a high volume production well is to be in-stalled, the well should be located farther than recommended from potential sources of contamination dueto its potentially large radius of influence. Ideally, in any situation, the owner of the well should (and, if itis a public supply, is required to) own all of the land within the isolation distance.

Areas of Known ContaminationIn areas of known ground water contamination, the water well driller should contact the local health

department or the Ohio EPA district office prior to drilling the well to determine if any special precautions/requirements are necessary to avoid drawing in the contaminants. Also, in some cases, it may be necessaryto drill a test well first to determine if a safe water supply can be obtained. If contaminated water isencountered above an aquifer containing potable water, the casing shall be extended to the bottom of theaquifer containing contaminated water or as deep as necessary to prevent the entry of contaminated water.Many times this situation occurs in shallow aquifers, which typically are most vulnerable to bacteriologi-cal contamination from surface water or chemical contamination from fertilizers, landfills, and surfacespills, etc. In nitrate-impacted areas, the levels of nitrates in the water supply may be reduced by increas-ing casing depths.

If contaminated water is encountered below an aquifer containing potable water, the lower portion ofthe well shall be filled with grout to a height sufficient to prevent the entrance of contaminated water intothe aquifer containing potable water. This situation may occur in wells where salt water from a deeperaquifer migrates upward and impacts the water quality of the shallower formation.

Proximity to Surface WaterThe Ohio EPA recommends a 50-foot set back from all sources of surface water to improvethe chances of obtaining a ground water designation for new wells. Private or non-potablewells should be located at least 25 feet from surface water sources.

Due to concerns with bacteriological contamination of water supplies, the USEPA requires each state todetermine the source of the water for all public water supplies. Sources designated as surface watersupplies are required to provide additional treatment to meet USEPA’s requirements. The Ohio EPA uses aWater Source Designation Worksheet to determine if the water supply meets the criteria to be classified asground water. The location of new wells should be selected to provide sufficient horizontal and verticalseparation from surface water bodies to ensure that they meet the separation requirements to be designatedas a ground water source. The final determination may be contingent on obtaining quarterly bacterialanalyses which are negative for coliform bacteria. The Ohio EPA Division of Drinking and GroundWaters (DDAGW) may be contacted for a copy of their complete guidance on source water designation.

Floodplain ConsiderationsIt is recommended that all wells in a floodplain be equipped with watertight surface sealsand be vented using a metallic pipe which extends to at least 3 feet above the one hundredyear flood level (see section on Well Completion for details on well vents in floodplains). Allcasing for community public water supply wells must be extended to at least 3 feet abovethe 100-year flood elevation, and either be mounded or equipped with work platforms and beprotected from floating debris. Extending only the casing may be accepted for non-commu-nity water supply wells.

No potable water supply wells should be located in a floodway unless the well is protected fromfloating debris, on a pedestal, and/or equipped with a watertight wellhead seal.

8

Sole Source Aquifers and Wellhead ProtectionThe aquifer protection requirements of the Safe Drinking Water Act amendments of 1986 established

procedures for designating areas where an aquifer is the sole or principal source of drinking water. Theseareas are commonly called Sole Source Aquifers and are defined as an aquifer which supplies 50% ormore of the drinking water for an area and may be designated by USEPA or by petition. The purpose ofthe designation is to prevent grants of Federal financial assistance to projects which may contaminate asole source aquifer and create a significant hazard to public health (40CFR, 1977). The USEPA can reviewany project which may have a significant impact on the environment and require that all available alterna-tives to the project be explored to minimize or eliminate the potential for contamination. There have beenfour areas designated as sole source aquifers in Ohio. These are the Great Miami/Little Miami River BasinBuried Valley Aquifer System, the Catawba Island Aquifer, the Pleasant City Aquifer, and the AllenCounty Area Combined Aquifer System. In addition, the Safe Drinking Water Act Ammendments of 1996require that all public water supplies establish a source water assessment and protection program whichdelineates the recharge areas within a five year time-of-travel to any public water supply well(s). Thisdelineated area is known as a source water assessment and protection area. An inventory of potentialsources of contamination within this area is required, along with protection strategies designed to mini-mize the potential for contamination from these sources.

Well Construction Materials and Equipment

Materials Used In The Drilling ProcessDrilling FluidAny drilling fluid (commonly referred to as drilling mud) used should meet American Petro-leum Institute Marsh funnel viscometer discharge requirements of one quart per 32 to 38seconds. Density of the mud, as measured by a mud balance, should be less than 9.0pounds per gallon. All drilling muds must meet ANSI/NSF Standard 61.

Drilling muds are a mixture of water, clay and often chemical additives used to lubricate and cool thedrill bits or other cutting tools, and to carry the cuttings to the surface of the borehole. They are also usedto stabilize the borehole and control fluid loss (Driscoll, 1986). For the drilling mud to function properly,its density and viscosity must be properly monitored, as well as the composition of the water used to makeup the mud. Contaminants such as calcium, chlorides (salts), and chlorine in the make-up water will affectthe performance of the drilling fluid. Drilling mud should be mixed according to the manufacturer’srecommendations, and include any treatments for the previously mentioned contaminants. Soda ash canbe added to counteract calcium concentrations of 150 parts per million (ppm) or greater, while chlorineconcentrations above 150 ppm can be removed by aeration. Water with chloride concentrations above 500ppm should not be used at all. Finally, drilling fluid should be removed from the borehole prior to andduring development of the well.

AdditivesAny additive used in the drilling, development, or grouting of a water supply must be de-signed for that purpose and meet ANSI/NSF Standard 61. Additives not recommended foruse include guar gum and biodegradable organic materials.

Drilling mud additives can include a variety of compounds, including chemicals as well as organic andinorganic materials. Phosphates, polymers, and clays are just some of the types of additives availabletoday. Phosphates are generally used as a cleaning material for the borehole and casing, and for corrosionand scale control. Use of phosphates should be kept to a minimum, and only in accordance with ANSI orNSF Standard 61. Polymers are generally used for lubrication and control of coagulation and flocculation.As with phosphates, the employment of polymers should be kept to a minimum and be used as approvedby ANSI/NSF Standard 61. Clays are generally naturally-occurring substances composed of fine-grainedmaterial that includes clays, shales, and other formations with a high clay content. Bentonite is a type ofclay that is commonly used in the drilling, grouting, and sealing processes of a water supply. The additivesnot recommended for use, i.e. guar gum and biodegradable organics, can promote the growth of bacteria ifnot removed from the well during construction and development. The well must be thoroughly cleanedduring well development and disinfected prior to testing if these additives are used.

9

LubricantsAll lubricants must meet ANSI/NSF Standard 61 and be easy to use. Lubricants must beable to be flushed from the borehole using standard practices and equipment.

Lubricants can consist of petroleum or vegetable-based oils, as well as drilling muds and pressurizedair. They are used to control friction and heat on the drill bits, and to help ease assembly of drill stems andother mechanical tools used in the borehole.

Drive shoeDrive shoes should be used when driving casing.

A drive shoe may be commercially made or can consist of a section of steel casing threaded or weldedonto the bottom of the driven casing. The drive shoe is generally hardened steel and has a beveled edge forcutting through rock or other hard, consolidated formations.

Materials Used To Construct A WellCasingSteel casing should be prime, minimum Grade A pipe or tubing. The minimum wall thicknessof steel casing should be no less than .188 inch, regardless of whether it is driven or set inthe borehole. However, larger diameter casing will require a greater minimum wall thickness.Steel casing should meet ASTM Standard A53, A106, or A589, and API Specification 5L. Allcasing for public water supply wells shall comply with the minimum wall thickness and otherrequirements of ANSI/AWWA Standard A100. Steel casing wall thickness may require anadditional allowance for corrosion. Tubing that meets the ASTM A500 standard must behydrostatically tested.

PVC (polyvinyl chloride) casing must meet ANSI/NSF Standard 14 for potable water or ANSI/NSF Standard 61 and ASTM F480; with a minimum wall thickness equivalent to SDR(standard dimension ratio) 21. Larger diameter (8" or greater) PVC casing may requiregreater thickness to meet collapse strength requirements. The manufacturer’s recommenda-tions for use should be followed, as collapse strength is a function of wall thickness.

Concrete casing must meet ASTM Standard C478 and C913.

Casing is generally a steel or PVC pipe used to line a borehole to prevent it from caving in and toexclude undesirable water, gases, or other liquids. A casing is required to extend a minimum of 25' belowgrade (unless geologic conditions warrant a variance) and a minimum 12 inches above grade. All steelcasing and related materials must meet appropriate ASTM, API, or ANSI/NSF standards, and be certifiedfor use with potable water. The use of casing materials other than steel for public water supply wells mustbe accepted by the Ohio EPA-DDAGW prior to installation. A determination will be made during well siteacceptance. Reject or used pipe should not be used in the casing or development of a potable water supply.

Selection and use of any casing should be based on acceptable and applicable standards and the envi-ronment to which the casing will be exposed. Additional criteria for casing selection may depend on thepresence of any contaminants. Suitable provisions should be made for the proper and clean storage of allcasing pipe. Plastic casing material should be stored where it is free from exposure to direct sunlight. Steelcasing should be prime pipe meeting the requirements of ASTM A53, A589, and API 5L with a minimumrating of standard tensile, hydrostatic, and collapse strength. Tubing meeting the requirements of ASTMStandard A500 may be used if the tubing is hydrostatically tested. Polyvinyl chloride (PVC) casing mustbe new pipe meeting the requirements of ASTM F480 and NSF Standard 14, or equivalent standards andhaving a SDR of 21 or below. All PVC casing must be NSF approved for potable water and well casingand should be so marked. Other types of casing would include casing made of materials such as concreteor similar composites. Use of other casings should be discouraged. However, if concrete casing is used ina well, the material must meet ASTM Standard C478 and C913, or related testing requirements and be ofsuch quality as to provide a safe container for potable water.

Casing JointsAll casing joints must be structurally sound, uniform, and watertight. Joints for concretecasing should meet ASTM Standard C990.

10

All joints should be threaded and coupled or welded. Joints can include use of butt-welds, band rings,flared joints, and welding collars. Butt welds should require use of welding collars and/or guides. Joints inconcrete casing should be constructed of rubber or mortar and installed according to the manufacturer’srecommendations.

Threaded pipe must be reamed and drifted and tightly sealed.

Use of threaded couplings is acceptable. All threaded pipe and couplings must meet ASTM standardA53 or ASTM A589, API Standard RP 5B1, NSF Standard 14, or equivalent requirements.

For solvent welded joints, the manufacturer’s recommendations on cleaning and preparationof pipe and application of various solvents and cements must be followed. Spline-lockjoints, such as Certa-Lock, should comply with watertightness and mechanical strengthrequirements.

Integrity of all solvent welded joints is dependant on temperature and time requirements and properapplication of the solvent. All solvents must meet or comply with ANSI/NSF Standard 14, ASTM F480,or similar requirements. Other types of joints used include Certa-Lock or other snap-fit couplings thatprovide watertight connections and have the mechanical strength and integrity to withstand installationand borehole pressures. Joints between concrete casing sections will require use of rubber gaskets orother approved devices, or other sealants (e.g. mortar) meeting ASTM Standard C990.

LinersLiners must be watertight and meet NSF Standard 61 or similar requirements. Minimum wallthickness should be equivalent to SDR 26.

Liners are generally used in addition to or in conjunction with approved casing. Use of liners in wellswill require extension of the liner up to the bottom of the pitless adapter so that it will be visible from theground surface.

GroutGrout should consist of a high solids (15-30%) high-yield sodium bentonite product or neatcement and meet ANSI/NSF Standard 61. Neat cement should meet ASTM Standard C150.Each should be mixed and installed according to the manufacturer’s recommendations. Insome circumstances, concrete can be used as a grouting material. Concrete should also bemixed and installed according to the manufacturer’s recommendations.

Grout is a material consisting of neat cement or bentonite that has a very low permeability and isacceptable for use with potable water. Grout is placed in the annulus, the space between a borehole and thewell casing, to seal out unwanted water or other fluids. Grout is placed from the bottom of the casing up tothe top of the borehole when an oversized borehole is drilled. When the casing is driven, the grout will becarried down with the casing as it advances. Grout must be as approved by ANSI/NSF Standard 61 orsimilar requirements and must be mixed and used in accordance with manufacturers’ recommendations.

High solids bentonite slurries include bentonite, water, and sometimes additives such as polymers, thathave been mixed to specific weights and standards. High solids bentonite grout typically has a solidscontent of 15% to 30%, unlike drilling mud, which typically has a solids content of only 3% to 6%(Oliver, 1997). High solids bentonite grout is generally pumped to the bottom of the casing or top of thegravel pack and forced up to the top of the well to provide a watertight seal between the borehole andcasing. All bentonite grout materials should be mixed and used according to the manufacturer’s specifica-tions. Dry granular bentonite should be used to seal driven casing, except where the joints are butt weldedtogether. Butt welded joints will not carry the dry granular bentonite down the hole as readily as flared orcoupled joints. Therefore, it is recommended that if butt welded joints are to be used, then an oversizedhole should be drilled so that the casing can be set in the borehole then grouted. Dry granular bentonitecan also be used to seal a total annular space of four inches or more if the casing is 100 feet deep or less(see the section on Geological Considerations).

Neat cement slurry is Portland cement with no aggregate, and water. It usually takes 48 hours to cureand generates considerable heat (heat of hydration) during the curing process. Attention must be paid tothe depths that neat cement will be used and the type of casing installed. Enough heat can be generatedduring the curing process to melt PVC casing pipe. Neat cement also has a tendency to shrink and crack.Bentonite can be added at a content of 3% to reduce the cracking problem, but it will not prevent shrink-age (Smith, 1994). Care must also be taken when using additives such as calcium. Calcium will reduce

11

setup time, but will also increase the heat of hydration. Neat cement should be pumped into place, notgravity fed, due to its tendency to separate in water.

Use of concrete as an annular sealant is not recommended unless it is installed through a tremie tube.Concrete grout is very abrasive on plastic; if this type of grout is used on a routine basis, the tremie pipeused for installation should be metallic. Like neat cement, concrete should be pumped into place to avoidseparation problems in water.

Materials not suitable for use as grouting material include fireclay and cuttings. Fireclay and cuttingsparticles can range in size from nearly powder to chunks almost an inch across. The inconsistent size,moisture content, and plasticity of these materials make them generally unsuitable for use as a groutingmaterial. Unpredictable and uncontrollable bridging of materials also can occur.

ScreensA screen should have enough uniform openings to create at least 8% (preferably more)open area per foot of screen, and to maintain an entrance velocity of 0.1 foot per second.The screen materials and construction method need to provide sufficient column andcollapse strength to withstand installation and borehole pressures. Plastic screen materialsshould meet ANSI/NSF Standard 61. The use of handmade or hand-cut screens is notrecommended. Mild steel screens tend to have short working lives in most environmentsdue to rapid corrosion; therefore, their use in water wells is not recommended.

A screen is an intake structure with uniform openings designed to retain the formation, prevent collapseof the borehole adjacent to the screen, accommodate a yield adequate for the intended use of the well, andmaximize the life of the well. Screens should have a minimum of 8 percent open area, constructed of non-clogging slots. Open areas of 30-40 percent are common for continuous slot screens without any loss inscreen strength. Screen openings should be continuous around the screen with screen openings V-shapedand widening inward to facilitate development and enhance screen life. The screen materials and construc-tion need to provide sufficient column and collapse strength to withstand installation and emplacementpressures. Screen materials should be selected to resist corrosion. Mild steel screens typically undergorapid corrosion, and are not generally recommended for use in water wells. Where metal screens will beused, screen materials that are the same as the casing materials should be used to minimize corrosion dueto dissimilar metals being in contact with each other. Metal screens may also be joined to PVC casing.PVC screens may be attached to metal casing with the use of appropriate couplers (NGWA, 1998).

Screens must facilitate well development, have a low head loss through the screen, control the entranceof fine-grained materials, and be resistant to incrusting and biofouling (Driscoll, 1986). The majority ofscreens used today are made from stainless and carbon steel, and PVC. Screens are generally madefollowing four basic designs. These are: continuous-slot, wire-wrapped, machine-slotted, and louvered.

The proper selection of the screen size openings and screen length must be determined by the wellcontractor based on the aquifer type, aquifer grain size and uniformity coefficient, the desired volume orflow of water, size of pump, depth of the well and other considerations. The experience and expertise ofthe contractor also plays a role in proper screen selection. To maximize well efficiency and screen designlife, the percent open area of the screen should be roughly equivalent to the porosity of the aquifer.Screens with large open areas typically have low entrance velocities, and subsequently less encrustationand greater resistance to corrosion. Five general steps should be followed in selecting the screen sizeopenings and length: 1) perform a grain size analysis either visually or using sieves; 2) decide to naturallydevelop or gravel pack the well; 3) select a slot size using the 50/50 rule; 4) determine the screen diameterand length; and 5) check the entrance velocity using the manufacturer’s curves. In order to obtain the bestwell design, a sieve analysis should be performed on the aquifer materials to determine the effective grainsize and uniformity coefficient of the aquifer materials to help select the correct screen size opening and/or determine the need for a filter pack. Driscoll (1986) provides a discussion of determination of effectivegrain size and uniformity coefficient, and both Driscoll (1986) and U.S. EPA (1975) provide recommenda-tions on screen size selection based on aquifer conditions.

Gravel Pack/Filter Pack/Formation StabilizerGravel pack/filter pack/formation stabilizer materials should consist of well-rounded particles,95% siliceous, that are smooth, uniform, free of foreign matter, properly sized, washed, anddisinfected. Pack material should extend 40% of the screen length above the screen, or aminimum of 2 feet for wells 6 inches in diameter or less, and a minimum of 4 feet for wellsgreater than 6 inches in diameter, to allow for settling after development. The gravel pack

12

should be no less than 3 inches thick, and no greater than 8 inches thick, due to difficultiesrelated to proper well development.

A gravel pack generally consists of small, well-rounded sand or gravel that has been washed andcleaned of fines and any foreign materials. Where the aquifer materials are non-homogeneous, the unifor-mity coefficient of the aquifer is less than 3.0 and the effective grain size is less than 0.01 inches, a filteror gravel pack should be used (U.S. EPA, 1975).

All gravel pack materials should be disinfected prior to placement in the well to prevent contamination.Gravel for gravel packs can be purchased pre-chlorinated, but the well will still require chlorination. Thegravel pack is placed between the well screen and the borehole wall to prevent fine materials from passingthrough the screen and entering the well. The gravel pack also helps prevent clogging of the screen by thisfine-grained material.

Unless clean gravel pack materials are purchased for each well, the contractor must provide a cleanstorage area free from contamination. Approved gravel pack sand and gravel is available from varioussupply companies.

The gravel pack should be installed from the bottom to the top of the well screen by slowly pouringdown the annular space, or tremied with water, to prevent separation and bridging. Installation of a gravelpack above the well screen may make a well more difficult to disinfect. Contamination from bentonitegrouting materials can be avoided by extending the gravel pack above the screen by a minimum of 15% oraccording to the guidelines specified above, and by the placement of 6-12 inches of bentonite pellets ontop of the gravel pack prior to regular grouting.

PackersPackers should be made from inert materials such as rubber, neoprene or other materialsthat meet ANSI/NSF Standard 61. Packers should be used with telescoping well screens.

A packer is generally used to form a seal between a telescoping well screen and the well casing, or thecasing and the borehole wall. Most packers are now made from neoprene or similar inert materials. Theuse of lead must be prohibited. Packers should be approved for use with potable water and should meet therequirements of NSF or similar industry standards.

Well Construction Procedures

General ProceduresThere are many procedures which are common to all types of well construction. These procedures deal

with subjects involving minimum siting requirements, plumbness and alignment of the borehole, mini-mum casing depths and diameters, gravel pack, and grouting the annular space. Minimum siting require-ments were discussed earlier in this document (see pp. 3-7). However, it should be noted that, duringdrilling, it is very important that the selected well site be maintained in a secure and sanitary manner toprevent contamination of the well. All materials used during well construction should be kept clean andnot placed directly on the ground to minimize the potential for contamination. All wells intended to bevertical wells should have boreholes that are sufficiently plumb and straight to receive the casing withoutbinding (U.S. EPA, 1975). The plumbness can also affect the performance of some types of pumps, suchas turbine pumps, which need a fairly straight borehole to operate properly (Driscoll, 1986).

CasingMinimum casing depth for all wells should be 25 feet below ground surface.

Some geologic conditions may dictate that there be less than 25 feet of casing set (see GeologicalConsiderations for a more detailed discussion of exceptions), but in no instance should there be less than15 feet of casing set in the borehole. Wells developed in shallow aquifers should require variances fromappropriate regulatory agency to allow less than 25 feet of casing to be set in the well.

The minimum casing diameter for a well is largely determined by its use and the aquifer in which is tobe developed. For most domestic wells, a diameter of 5" is sufficient to provide an adequate householdsupply, and allow easy installation and maintenance of the pumping equipment. Well diameters of lessthan 5" are not recommended for any use. Drilling (as opposed to driving, jetting, or excavating) is therecommended method of well installation.

While some driven wells are only 2" in diameter, their use should be limited to specific geologicconditions (see section on Geological Considerations). Industrial or public supply wells, on the other hand,

13

may have diameters of 12" or larger to allow more water to be pumped from the wells to satisfy greaterwater demands. However, some wells may have larger diameters to allow for storage in the borehole if theaquifer in which they are developed yield little water. Consequently, the intended use of the well, and thenature of the aquifer, are critical factors in determining the diameter of casing to be used in a well. Formore information on how to estimate water needs for a house, industry, small public supply, etc., pleasesee Table 1 in Appendix III.

Filter Pack/Formation StabilizerThe annular thickness of the filter pack should range between 3 and 5 inches. The filter packshould extend above the screen a distance equivalent to 40% of the total screen length, or aminimum of 2 feet in wells 6 inches in diameter or less, and a minimum of 4 feet in wellsgreater than 6 inches in diameter, to account for settling and loss during development, andto avoid contamination from the grouting material used.

Filter pack, also known as gravel pack, is used when well screens are installed. It consists of clean sandor gravel of selected size and gradation which is installed in the annular space between the screen and thewall of the well bore. As discussed previously, the particles should be well-rounded, of 95% siliceousmaterials, and be smooth, uniform, free of foreign materials, properly sized to the slot openings of thescreen used (90% of the filter pack material should be retained), washed, and disinfected. The filter packshould not be extended above the minimum casing length, except in temporary dewatering wells. Truefilter packs are typically used in large diameter, high capacity production wells, such as a municipalsupply well.

In Ohio, what is commonly called gravel pack in domestic wells is really a formation stabilizer. Theannular thickness of the formation stabilizer is usually no more than 2 to 3 inches, with nearly 100% of thestabilizer material retained by the screen. The stabilizer materials are similar to what is used for the filterpacks, and they can be installed by the same methods. Due to their coarse nature, the formation stabilizershould extend at least two feet above the top of the screen in wells 6 inches or less in diameter. Formationstabilizers can also be used with perforated liners in wells developed in incompetent bedrock formations.

GroutingThe annular space in all wells should be grouted, regardless of the method of construction.When the drilling method involves drilling an oversized borehole, it is recommended thatwells up to 14 inches in diameter have a minimum of 2 inches of total annular space. Forwells greater than 14 inches in diameter, the minimum total annular space should be 4inches. Grout should be pumped into place through a tremie tube from the bottom of thecasing, or top of the gravel pack, to the ground surface. When the drilling method involvesdriving the casing, the dry driven method of grouting should be used.

Grouting procedures will vary by drilling method (more information on drilling methods used in Ohiocan be found in Appendix I). However, there are general procedures that apply to most drilling methods(see Geologic Considerations for exceptions).

Cable Tool/Driven Casing HammerSingle-cased wells drilled by the cable tool or driven casing hammer method should be grouted using

the dry driven grout method. If the well is double-cased, then the annular space between the inner andouter casing should be grouted, and the outer casing removed (see Figure 3). If the outer casing is toremain in place, it should be dry driven grouted as it is installed. For public water supply wells, the OhioEPA will accept the use of the dry driven method of grouting. The construction of the well must followthe recommendations in this document (including the use of welded flare joints or collar joints, and a driveshoe). However, under certain circumstances (i.e. where bacteriological or chemical contamination of anupper aquifer exists, areas of shallow bedrock, or for wells greater than 10 inches in diameter) it is recom-mended that the well be drilled with a larger temporary outer casing and the annular space grouted with atremie pipe while the outer casing is being removed. Another acceptable method is to use temporary grouttubes which are driven along the well casing to allow grout to be injected into the annular space while thetubes are being withdrawn. This will ensure that the annular space is sufficiently grouted to the nativesoils/rock materials.

Rotary (Mud and/or Air)/Percussion HammerWells constructed using rotary or percussion hammer methods should be pressure grouted because

these drilling methods create a significant annular space. As stated earlier, the minimum total annular

14

space for wells up to 14 inches in diameter should be 2 inches (Figure 4a). Wells greater than 14 inches indiameter should have a minimum total annular space of 4 inches (Figure 4b). If the total annular space isgreater than 4 inches and the well depth is less than 100 feet, then, regardless of the diameter of the well,the annular space can be sealed with bentonite chips if there is a minimal amount of water in the borehole.Water should then be added to hydrate the chips. If there is a problem getting a tremie tube to the bottomdue to narrowing or blockage of the annular space, the well should be grouted using the displacementmethod. The displacement method involves filling the inside of the casing with the grouting material, thenforcing it down through the bottom of the casing and into the annular space.

Auger (Hollow Stem, Solid Stem, Bucket)/Reverse Circulation RotaryWells constructed with a hollow stem auger should be grouted using the methods as mud/air rotary-

drilled wells (see Figure 5). For solid stem auger, bucket auger, and reverse-circulation rotary-drilled wellscompleted in unconsolidated formations, the grout must be placed from the top of the filter/gravel packto the surface. A minimum of 25 feet of casing and grout, or casing and grout to the top of the aquifer isrecommended. Bentonite chips can be used when the total annular space is greater than 4 inches, there isminimal water in the borehole, and the total depth is less than 100 feet. Again, water should be added tohydrate the chips.

DrivenDriven wells, such as well points (Figure 6), should be grouted using the dry driven grout method (see

Appendix II for fact sheet on dry driven grout method). Geologic or working zone (non-potable wells)conditions may dictate the length of casing used.

JettingThis method is not recommended for permanent well installation. An oversize borehole should be

drilled, then surface casing should be set and grouted. Temporary installations will need 5 feet of surfaceseal.

Secondcasingstring

Wellscreen

Firstcasingstring

Sand &gravelaquifer

grout Grout

DriveshoeDrive

shoe

Coupling

Granularbentonite

grout

Bedrockaquifer

Casing

Figure 3. Examples of recommended well construction using cable tool drilling methods.

15

Well Casing5" to 14"

Sandy Soil

Clay and Sand

Sand

Clay

Sandy Clay

Coarse Sand & Gravel

Filter pack/formationstabilizer should extend2 to 4 feet above screen.

Bentonite Grout

Well Screen

1"1"

Well Casinggreater than 14"

Sandy Soil

Clay and Sand

Sand

Clay

Limestone

Bentonite grout – slurry orchips if total annular spaceis greater than 4"

2" 2"

Packer

Figure 4a. Example of recommended rotary-drilled well construction for wells developed in unconsolidatedformations–total annular space 2 inches or more.

Figure 4b. Example of recommended rotary-drilled well construction for wells developed in consolidated forma-tions–total annular space 4 inches or more.

16

Large Diameter Excavated WellsLarge diameter wells that are installed by a variety of excavat-

ing methods must have a minimum of 1 foot of bentonite installedin the annular space. The bentonite should be chips or pellets andshould be installed on top of a layer of pea gravel. The pea gravelwould be installed on top of the gravel pack above the formationsupplying water. The bentonite will need to be hydrated if locatedabove saturated conditions in the soil. The annular space should bebackfilled to the surface with clean, impermeable clays andrecompacted as much as possible. The top of the well should befinished with an impermeable surface seal sloping away from thewell and extending beyond the edges of the excavation.

The general well construction procedures discussed here maychange, depending on the geologic conditions encountered whiledrilling the well. The next section will discuss what geologicconditions could influence the construction procedures, and whatchanges in the procedures would be necessary.

Geological Considerations

Unconsolidated FormationsThe use of unconsolidated geologic formations for water

supplies is very common throughout Ohio. Unconsolidated forma-tions consist of rock and mineral fragments that have been depos-ited in layers but are not cemented or are only partially cementedtogether. Ground water flows through the pore spaces between thegrains of an unconsolidated formation. Unconsolidated formationsin Ohio often form very productive aquifers with yields rangingfrom 100 to over 1000 gallons per minute. These aquifers are

Sand filter pack

Coarse-gradebentonite

Well sealed fromtop of coarse-grade bentonitelayer to surfacewith slurry.

Completed WellCasing and ScreenInstalled with Sand

Filter Pack

Pilot AssemblyRemoved

Advancing HollowStem Auger withPilot Assembly

Drill Rod WellCasing

Augercuttinghead

Pilotassembly

Sandpack

Wellscreen

Figure 5. Example of well construction using hollow stem augers. (Modified from Hackett, 1987 and 1988)

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screen

drive point

casing

granularbentonite

grout

Figure 6. Example of recommendeddriven well construction.

17

primarily composed of layers of sand and gravel deposited from meltwaters from glaciers that oncecrossed Ohio. Unconsolidated aquifers are found in several hydrogeologic settings including buriedvalleys, moraines and kames, and current river valleys. Buried valley aquifers are remnants of channelscut into bedrock by rivers that flowed prior to or between periods of glaciation. These valleys subse-quently filled with coarse sand and gravel deposits forming thick, productive aquifers. Modern rivers oftenflow on top of these buried valleys providing a source of recharge to the aquifers. Sand and gravel lensesmay also be found in other glacially deposited features such as end moraines, beach ridges, kames andeskers. Alluvial deposits of sand and gravel may also be found in modern day river valleys.

CasingA minimum of 25 feet of casing is recommended. Where shallow aquifers overlie nonproduc-tive bedrock, less than 25 feet of casing may be used. Less than 15 feet of casing is notrecommended under any conditions.

In some areas of Ohio, shallow sand and gravel deposits overlie nonproduction bedrock formations.This is common in areas of northeastern Ohio in Lake and Ashtabula counties where beach ridge depositsoverlie non-water-bearing shales. These shallow aquifer conditions may necessitate the use of less than 25feet of casing to obtain water from a well. No less than 15 feet of casing is recommended for wells usedfor drinking water supply. Well points are often used in these types of formations, but are not recom-mended for use as drinking water supply.

ScreensWells completed in unconsolidated formations should use screens that meet the perfor-mance standards described on page 11. Minimum recommended length of a screen is 2 feetunless the formation is thinner. For maximum yield in an unconfined aquifer, the screenshould penetrate 30-50% of the formation. The bottom of the screen should be sealed.Where a telescoping screen is used, the screen must be attached either directly to thebottom of the casing or to a packer. For naturally developed wells in non-homogeneousaquifers, the slot size selected should retain at least 40-50 percent of the aquifer material.For artificially gravel packed screens, the slot size selected should retain between 85 and100 percent of the filter material.

The presence of large boulders or cobbles in some geologic formations may prevent the successful useof screens. In these situations, the use of a screen as recommended in the above standard may be impracti-cal. Conversely, in very fine sandy or silty formations, properly sized screens may be unable to prevent theentrance of the formation into the well. In these cases it may be necessary to use settling tanks or low flowdevices to prevent the entrance of sediment into the water system.

Filter Pack or Formation StabilizerThe use of a filter pack or formation stabilizer is recommended where the natural materialsare non-homogeneous and not conducive to proper well development, or may slough orcollapse in the borehole prior to development. The pack/stabilizer should not extend above15 feet below the ground surface.

GroutingThe annular space should be grouted from the top of the screen or filter pack to the groundsurface. Where the annular space is greater than 2 inches per side, is dry or has a minimalamount of water in the borehole, and the borehole depth is less than 100 feet, dry granularbentonite may be installed by pouring into the annular space (see Figure 7). The granularbentonite should be screened and poured slowly to minimize bridging, with periodic tamping.The volume of the annular space should be calculated and compared to the volume ofbentonite used as a check to make sure bridging in the annular space has not occurred.Water should be added to hydrate the bentonite.

PackersThe use of a synthetic packer is recommended with the use of telescoping well screens.

Geological IssuesIn very fine sandy or silty formations, properly sized screens may be unable to prevent theentrance of the formation into the well. In these cases it may be necessary to use settlingtanks or low flow devices to prevent the entrance of sediment into the water system. Inareas of extremely low yield or very thin, shallow aquifers, traditional drilled wells may not

18

provide adequate yield and large diameterexcavated well installations may benecessary. These wells should follow therecommendations for casing, grout andwell completion described in the appropri-ate sections of this document.

Wells Developed in Consolidated For-mations

Consolidated formations in Ohio consist oflimestones and dolomites, shales, and sand-stones. Ground water in these formationsoccurs and moves primarily in fractures andbedding planes that are often interconnected.Yields from these aquifers vary significantlywith relatively poor yields from shales andshaley limestones (less than 5 gallons perminute), moderate yields from sandstones andsome limestones/dolomites (5-100 gallons perminute), and moderately high yields fromhighly fractured limestones and dolomites(greater than 100 gallons per minute).

CasingA minimum of 25 feet of casing is recom-mended.

LinersPerforated liner casing may be used tomaintain the integrity of the boreholewhere formations are prone to collapse,but perforations must not occur within 25feet of the ground surface. Liners must besecurely attached to the permanent casing.

In areas of southeastern Ohio, thin, alternating beds of limestones, shales, sandstones and coals providelow yields to wells. Wells are often drilled to penetrate multiple aquifers to maximize yields. Some ofthese formations are prone to collapse, necessitating the use of perforated liners.

GroutWells should be grouted from the bottom of the casing to the surface using the groutingmethod recommended for the method of drilling.

Geologic IssuesSome fractured or cavernous formations in Ohio may contain sediment that enters the well.Development procedures may be unable to entirely clear the sediment from these fractures,therefore it may be necessary to use settling tanks or low flow devices to prevent the en-trance of sediment into the water system.

Wells Developed in Unconfined AquifersUnconfined aquifers occur where the ground water in the geologic formation is open to the atmo-

sphere through openings in the overlying materials (Figure 8). The water level in the aquifer is referred toas the water table. These formations are readily recharged by precipitation, and are often hydraulicallyconnected to surface water bodies.

CasingA minimum of 25 feet of casing is recommended, with no less than 15 feet of casing whereshallow aquifers are present.

Coarse meshscreen Total annular space

greater than 4 inches

Finer particlesfiltered out to

prevent bridging

A minimalamount of water

in the casing

Total depth ofannular spaceto be groutedmust be lessthan 100 feet.

Figure 7. Grouting the annular space of wells withcoarse grade bentonite products using thepouring method. (Modified from WisconsinDepartment of Natural Resources, 1993)

19

ScreensFor maximum yield in an unconfined aquifer, the screen should penetrate 30-50% of theformation.

GroutWells should be grouted from either the bottom of the casing or the top of the filter pack tothe surface using the grouting method recommended for the method of drilling.

Geologic IssuesDue to their typically shallow nature, wells completed in unconfined aquifers may need agreater isolation distance from known or suspected sources of contamination.

Wells Developed in Confined AquifersA confined aquifer occurs when the aquifer is separated from the atmosphere at the point of discharge

by a relatively impermeable geologic formation (Figure 8). Pressures in a confined aquifer are greater thanatmospheric pressures. The water level in a well penetrating a confined aquifer will rise to a level equiva-lent to the pressure head, or elevation within the aquifer. If this elevation is greater than the land surface,then the well will flow.

CasingThe casing length should be a minimum of 25 feet and should extend to the bottom of theconfining layer.

ScreensFor maximum yield in a confined aquifer, the screen should penetrate 70-80% of the forma-tion. The screen should be sealed at the bottom.

GroutThe well should be grouted from either the bottom of the casing or the top of the filter pack(where present) to the ground surface. All annular spaces adjacent to the confining layershould be grouted to maintain the integrity of the confining layer.

Filter Pack/Formation StabilizerFilter pack or formation stabilizer should not extend significantly into the confining layer, andshould not be placed across a confining layer allowing the interconnection of two aquifersalong the annular space.

Recharge Area

PotentiometricSurface of ConfinedAquifer Flowing Well in

Confined Aquifer Ground Surface

Well in Unconfined Aquifer Non-Flowing Well inConfined Aquifer

Confined Aquifer

Confining Layer

RegionalWaterTable

Confining Layer

Unconfined Aquifer

Water Table

Perched Water Table

coarse grade bentonite products using the

20

Geologic IssuesThe integrity of the confining layer should be maintained in all aspects of the well construc-tion and materials to prevent mixing of water between aquifers.

Wells Penetrating Multiple AquifersA variety of geologic conditions can lead to the presence of multiple aquifers. In the glaciated areas of

the state, sand and gravel lenses may overlie bedrock formations with both formations providing adequateyields to wells. In eastern and southeastern Ohio, wells are typically completed as open boreholes pen-etrating cyclic interbedded sandstone, limestone, shale and coal sequences in order to obtain adequate wellyields. Wells that penetrate multiple aquifers may allow the mixing of waters having different waterquality or the loss of water to another zone due to differences in hydraulic heads between the aquifers.Consideration should be given to the well yield required, the relative thickness of the aquifers, the pres-ence of multiple confining layers, and the hydraulic interconnection between the aquifers. In some areas,shallow zones of poorer water quality may exist that will need to be cased off to prevent contamination ofother aquifers.

CasingThe casing length should be a minimum of 25 feet and should extend to the bottom of theconfining layer. Known zones of poor water quality or contamination should be cased off andproperly grouted to prevent contamination of other aquifers.

GroutThe well should be grouted from the bottom of the casing or top of the filter pack/formationstabilizer to the ground surface.

LinersPerforated liner casing may be used to maintain the integrity of the borehole where forma-tions are prone to collapse, but perforations must not occur within 25 feet of the groundsurface. Liners should terminate within sight of the bottom of the pitless adapter or theground surface. Liners should not be open to more than one aquifer if water quality andhydraulic head vary between aquifers.

Geologic IssuesTo prevent the interconnection of two water-bearing zones having different water quality,completing wells in multiple aquifers is not recommended. Wells completed in multipleaquifers may also allow the thieving or loss of water to a lower zone due to differences inhydraulic heads between the aquifers. Exceptions to multiple aquifer completions occurwhere it is necessary to penetrate multiple zones to obtain adequate yields, particularly inareas of thin-bedded, cyclic formations (see Figures 9a and 9b).

Special Geologic ConditionsOther types of special geologic conditions occur across the state that may significantly impact well

drilling and construction procedures. Special care must be taken in these areas to prevent ground watercontamination and/or the loss of hydraulic head in confined or semi-confined aquifers.

Flowing WellsFlowing wells occur where the hydraulic head in a confined aquifer is at an elevation greater than the

land surface. Flowing wells can cause problems related to the drilling of the well when attempting to setcasing and perform grouting. Flowing wells are common in some areas of northwestern Ohio, and inglaciated areas of the state where relatively impermeable glacial till overlies productive sand and gravelaquifers.

CasingCasing should be installed through the confining layer into the top of the aquifer that isproducing flowing conditions. The selection of casing materials must take into account anyhydraulic pressures on the casing that will occur due to the flowing aquifer conditions.

GroutThe well must be properly grouted from either the bottom of the casing or the top of the filterpack (where present) to the land surface.

21

Well CapMinimum 25 feetof Well Casing

SandySoil

Clay & Sand

Sand Aquifer

Sand & Gravel Aquifer

Bentonite Grout

Clay

Formation Stabilizeror Filter Pack

Figure 9a. Recommended well construction for wells penetrating multiple unconsolidated aquifers.

Well CapMinimum 25 feetofWell Casing

Soil

Shaley Sandstone

Sandstone

Shaley Sandstone

Sandstone

Bentonite Grout

Shale

Drive shoe, shale trap, orpetal steel basket

Figure 9b. Recommended well construction for wells penetrating multiple consolidated aquifers.

22

Grouting may be performed using several methods depending on the method of drilling and the rate offlow. Where flows are not excessive, double weight bentonite grout may be tremied into the annular spaceto prevent flow up the annular space in the borehole. The well may also be pumped to lower the waterlevel in the borehole to allow the placement of a filter pack and the installation of double weight bentonitegrout. Where flows are excessive, an upper enlarged borehole should be installed into the confining layerand pressure grouted. If the confined aquifer is consolidated, the inner casing should be driven or a smallerdiameter borehole drilled and the casing set firmly into the bedrock. The annular space around the lowercasing can then be pressure grouted using a double weight bentonite slurry (Figures 10a and 10b). If theconfined aquifer is unconsolidated, then a smaller diameter borehole should be drilled, with the casing andscreen installed into the confined aquifer. The well should be double cased and the annular space pressuregrouted using a double weight bentonite slurry (Figures 11a and 11b). Another method that may be usedto control flowing conditions is to set a surface casing, install a packer at the bottom of the casing, installthe inner casing, and pressure grout through the packer between the two casings.

Well CompletionFlows from the well should be restricted if possible to prevent the loss of hydraulic head inthe aquifer. An air gap should be used to prevent backflow into the well, and should be aminimum of 8 inches above the surrounding grade. A backflow prevention assembly with adouble check valve may be installed, in lieu of the air gap, if necessary. The air gap shouldbe a minimum of 8 inches above the ground, with a minimum of 2 inches of air space, or aminimum of 2 pipe diameters. Overflows discharging into a drainage channel or catch basinshould have a minimum air gap of 2 overflow pipe diameters above the flood rim of thereceiving basing. Overflow should not be discharged to a septic system.

Cavernous or Highly Fractured FormationsCavernous and highly fractured formations are present in limestones and dolomites in northwestern and

mid-central Ohio. Cavernous zones form where ground water has dissolved the limestone or dolomite andenlarged fractures or bedding planes to form large voids in the subsurface. The presence of these cavern-ous or highly fractured zones can affect the ability to properly grout the well, and may be a source ofsediment or poorer quality water, especially if these zones are interconnected to the land surface. If thewater from the well becomes turbid after a significant precipitation event the well may be under the directinfluence of surface water and may be contaminated with bacteria. Where cavernous or highly fracturedzones are encountered during drilling, the use of a downhole camera or caliper log may be useful toidentify the exact depths and nature of these zones to facilitate proper grouting and casing of the well.

CasingA minimum of 25 feet of casing is recommended. Any cavernous or highly fractured zonesthat are not being used as a source of ground water for the well should be cased off.

GroutThe well must be properly grouted from the bottom of the casing to the land surface. Anycasing installed through cavernous zones must be properly grouted. If the cavernous orhighly fractured zone is below 25 feet from the ground surface, then the zone can be filledwith cuttings or clean gravel, and then pressure grouted to the surface (Figures 12 and 13).

A shale basket, petal steel basket or rubber packer may be used to seal off cavernous or highly frac-tured zones. Where the cavernous or fractured zone is to be used as the source of water, these devices maybe installed at the top of the zone and annular space can be pressure grouted from the top of the zone to theground surface. Where cavernous or fractured zones are to be cased off, these devices must be installed atthe top and bottom of the zone, and the well cased and pressure grouted. In some cases, it may be possibleto pull the tremie pipe above the cavernous or fractured zone and then continue with pressure grouting.

ScreensA well screen may be installed adjacent to water-producing cavernous zones to stabilize theborehole and to prevent sediment from entering the well.

Mine Shaft/Abandoned Mine WellsWells penetrating abandoned underground mines often occur in areas of southeastern and eastern Ohio.

23

Step A. An outerenlarged drillhole2" larger than outercasing is drilledinto the middle ofthe confining bed.

Step B. Outercasing set tobottom of outerdrillhole. Annularspace is sealed.

Step C. An innerenlarged drillholeis drilled throughconfining bed totop of the aquifer.

Step D. Innercasing set to topof aquifer andsealed in place.

Step E. Opendrillhole isconstructed intoaquifer.

Step A. Temporary outercasing 4" larger thancasing diameter is driveninto the confining bed,or a larger diameterborehole is drilled.

Step B1. Permanentcasing pipe set to bottomof temporary outercasing, or enlargedborehole. Annular spaceis sealed. Temporarycasing is removed.

Step C. Openborehole drilled intobedrock aquifer.

UnconsolidatedOverburden

UnconsolidatedConfining Bed

ConfinedBedrock Aquifer



Step B2. Permanentcasing is driven throughremainder of confiningbed into aquifer.

Minimum of 25 feet ofpermanent casing

Minimum of 25 feet ofpermanent casing

ConfinedBedrock Aquifer

Gro

ut

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ut

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ut

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ut

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ut

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ut

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ut

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ut

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ut

Figure 10a. Rotary method for flowing well construction-confined bedrock aquifer with an unconsolidated confin-ing bed.

Figure 10b. Cable tool method for flowing well construction-confined bedrock aquifer with an unconsolidatedconfining bed.

24



UnconsolidatedConfined Aquifer

Filter Pack/Formation Stabilizer



UnconsolidatedConfined Aquifer

Step A. An outerenlarged drillhole 2"larger than outercasing is drilled intothe middle of theconfining bed.

Step B. Outercasing set tobottom of outerdrillhole. Annularspace is sealed.

Step C. An innerenlarged drillholeis drilled throughconfining bed intothe aquifer.

Step D. Innercasing (25'minimum) andscreen are setinto aquifer.

Step E. Filterpack/formation stabilizerplaced around screen,and annular space is thensealed from top ofpack/stabilizer to surface.

Minimum of25 feet of

permanentcasing

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ut

Gro

ut

Gro

ut

Gro

ut

Gro

ut

Gro

ut

Gro

ut

Gro

ut

Gro

ut

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ut

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ut

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ut

Step C. Screeninstalled, casing pulledback to expose screen.

Step B2. Permanentcasing is driventhrough remainderof confining bedinto aquifer.

Step A. Temporary outercasing 4" larger thancasing diameter is driveninto the confining bed,or a larger diameterborehole is drilled.

Step B1. Permanent casingpipe set to bottom oftemporary outer casing, orenlarged borehole. Annularspace is sealed. Temporaryouter casing is removed.

Figure 11a. Cable tool method for flowing well construction-confined unconsolidated aquifer with an unconsoli-dated confining bed.

Figure 11a. Rotary method for flowing well construction where both confining bed and aquifer are unconsolidated-double casing construction.

25

Tremie pipe

Annular space filledwith grout

topsoil

Clay or shale

grout

Shale basket, petal steelbasket, or rubber packer

Fracturedbedrock aquifer

aaaaaaa

aaaaaaaa

a

aaaaaaaMinimum of 25feet of casing

TopsoilTremie pipe


topsoil

Clay or shale

grout

Shale basket, petal steelbasket, or rubber packer

Fracturedbedrock aquifer

a

a

aaaaa

aaaaaaaa

aa

aaaaaaaMinimum of 25feet of casing

Shale basket, petal steelbasket or rubber packer


Topsoil

Shale

Shale

Fractured bedrock aquiferwith poor quality water

Figure 12. Recommended grouting procedures forwells penetrating fractured or cavern-ous formations.

Figure 13. Recommended grouting procedures forwells penetrating fractured or cavernousformations where an upper fractured orcavernous zone has been sealed off.

Water quality can vary, but is often poor depending on whether or not the entire seam is submerged. Wellscompleted in mines encounter conditions during drilling and construction similar to those found in cavern-ous formations.

CasingA minimum of 25 feet of casing is recommended. Any mines that are not being used as asource of ground water for the well should be cased off.

GroutThe well must be properly grouted from the bottom of the casing to the land surface. Anyproduction casing installed through mines must be properly grouted.

A shale basket, petal steel basket or rubber packer may be used to seal off mines. Where the mine is tobe used as the source of water, these devices may be installed at the top of the opening and the annularspace can be pressure grouted from the top of the zone to the ground surface. Where mines are to be casedthrough, these devices must be installed at the top and bottom of the void, and the well cased and pressuregrouted.

ScreensA well screen may be installed in water-producing mines to prevent sediment from enteringthe well.

26

Brine-Producing FormationsBrine-producing zones may be encountered in some areas of eastern, northeastern, southeastern, and

southwestern Ohio counties. These zones may occur due to the presence of natural brine in the formation,or contamination from oil and gas drilling, or abandoned oil and gas wells.

Geologic IssuesWhen these zones are encountered in a well, the well should be plugged back to an eleva-tion where the brine producing zones are not present. Plugging materials that are notadversely affected by the brine water (e.g. Hole Plug) should be used to seal back theborehole. If a brine-producing zone cannot be successfully sealed off, then the entire wellshould be properly sealed.

Gas-Producing FormationsGeologic formations that naturally produce methane gas can be found in confined bedrock formations

and some unconsolidated sand and gravel formations, especially in northeastern Ohio. The primary issuewith gas-producing wells is the need to properly vent the methane gas to prevent explosive conditionsfrom occurring in basements or other confined spaces. The installation of a holding tank may be necessaryto allow for volatilization of the gas to occur before the water is allowed to enter a building or home.Formations that produce methane gas should be cased off and the annular space properly grouted whereother water-bearing formations are present.

Well CompletionWells producing methane gas should be properly vented to the atmosphere to prevent theaccumulation of vapors and resulting explosive conditions. In some cases, a shroud may beinstalled around the intake of the pump to force the separation of the gas from the water.

Well Development ProceduresAll wells should be properly developed until turbidity in the well is minimized. Water pro-duced during development should not be discharged to a stream unless a NPDES permit isobtained, and controls are in place to prevent erosion and the discharge of turbid water.Smaller diameter wells will require an average of 1 hour of development per foot of screen.

Most of the drilling techniques used today can be classified as destructive drilling techniques. Theformation immediately around the drilled hole becomes compacted, drilling mud invasion and theformation of a mud cake on the borehole wall may occur, and/or fines may be driven into the forma-tion during the drilling process, all of which result in the loss of permeability in the formation. Inconsolidated rock formations, similar compaction may occur in poorly cemented rocks, and cuttingsor drilling mud can be forced into fractures and bedding planes that produce water. This in turn willcause the well to be very inefficient, especially if the intake portion of the well is not brought back tothe original values of aquifer porosity and permeability before the drilling process was started. Allwells should be properly developed and cleaned to reverse the damage caused by drilling to themaximum extent possible and to develop the well to maximize well yield and design life.

The purpose of well development is to reduce the compaction and intermixing of grain sizes thatoccurs during the drilling process, to remove any drilling muds from the borehole walls and theformation, or any mud cakes that may have formed, to increase the porosity and permeability of theformation adjacent to the screen or in the open borehole, and to created a graded zone of formationmaterials to prevent fines from entering the borehole (Driscoll, 1986).

The methods and techniques used during this process will be determined by the type of wellcompletion used, the type of screen and screen openings, the filter pack thickness (if present), theformation type, and the equipment available for the application. The methods are divided into twomajor categories: mechanical techniques and chemical techniques. All mechanical methods with theexception of high velocity jetting rely on the introduction of energy to disturb the natural formationor filter pack to remove the fines and allow them to be drawn into the well, with the remainingcoarser materials settling and supporting the screen. Mechanical techniques are typically divided intothe following classifications: mechanical surging, air surging or air lifting, overpumping andbackwashing, high velocity jetting, bailing, and hydrofracturing. Chemical techniques includeacidizing and the use of non-phosphorus-containing dispersants.

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Mechanical TechniquesMechanical SurgingInitial mechanical surging should be gentle, working 3 foot sections of the screen or openborehole at a time. Sediment in the well should be bailed out or removed periodically toprevent fine materials from reentering the aquifer.

This is the most commonly used development method for a cable tool rig and is the method thatrequires the least amount of equipment. A surge block is made to fit the inner diameter of the casing andcan be either solid or with a flapper valve. The block is made of layers of hard material with leatherwashers between them to effectively seal against the inner diameter of the casing. By raising and loweringthe block in the casing above the screen, a two-way washing action is created through the screen openings.This gentle surging action breaks up muds and removes fine materials from behind the screen, or cuttingsand fine materials that may be trapped in fractures in an open bedrock borehole. This material should beperiodically removed by a flapper-type bailer, a sand pump, or by air lifting. For fine formations and /orshallow wells, the surging action must be started slowly to avoid any wash out alongside the casing.Alternate surging and bailing should continue and gradually increase in vigor until the well is sand-free.

Air Surging or Air LiftingAir surging should be conducted at 1 to 2 times the design capacity of the well. Fine materi-als should be periodically removed by air lifting when the water becomes turbid. The wellshould be developed in 5 foot sections starting near the top of the screen or open borehole.Do not inject air into the screen. This method should be used cautiously with low-yieldingwells.

Compressed air may be used to develop wells in both consolidated and unconsolidated formations. Theair surging method uses compressed air injected into the well to lift water to the surface. The air is thenturned off, allowing the column of aerated water to fall back into the well, reversing flow back into theaquifer. This operation is performed repeatedly until the water is turbid; then the fine material must bebailed or airlifted from the well. The same two-way washing action achieved by mechanical surging canbe performed with this system. The discharge produced from airlifting is dependent on the air volumeavailable, the total lift required, the percent of submergence of the air line, and the annular area of thewell. Several criteria must be met for successful air surging/lifting and the airline and eductor pipes mustbe sized correctly. The airlift will only operate with minimum percentage submergence, generally 60% forwells with 100 to 200 feet of total lift required (Driscoll, 1986). Sufficient uphole velocities must bemaintained to discharge water and fine materials from the well. Driscoll (1986) lists the recommendedpipe sizes for airlift pumping. Air surging/lifting can be performed as a single pipe system open or closedto the atmosphere, or as a two-pipe system (U.S. EPA, 1975). Caution must be used when using the casingas the eductor pipe. Air should not be injected into the screens as this may cause the formation or gravelpack to be lifted upwards out of place on the outside of the screen. Do not place the air outlet at the bottomof the well to flush out the fines before the well has been thoroughly developed and the formation hassettled on the outside of the screen. In low yield wells with high static levels, the hole should not be blownat the start of the development procedure. This will blow all the water out of the well, creating a largepressure differential. There will be no support from the inside of the well to hold the loose formationslumping down, causing premature well failure to occur with the collapse of the casing or the screen.

Overpumping and BackwashingOverpumping and backwashing should be used alternately to achieve maximum develop-ment of the well. Overpumping should be performed in steps up to 1.5 times the designcapacity of the well.

The extra high velocities created by overpumping will cause the fine material to be washed in throughthe screen. This method results in a one-way flow and may lead to bridging or packing against the screen,which will limit the amount of development that can be performed by restricting the flow of fines into thewell. Most of the development will also only occur in the permeable zone adjacent to the screen. Thesehigh velocities are achieved by pumping the well with a pump that has a capacity of more than 10 timesthe anticipated flow rate of the well when in production. Overpumping is often combined withbackwashing to prevent bridging and compaction of the fine materials. This is achieved by switching offthe pump and allowing the water in the column to flow back down into the well. The non-return valve inthe pump must be removed to allow the backwashing action to occur.

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There are obvious limitations to this system. There has to be enough head of water in the column togenerate enough pressure for sufficient backwashing to occur. If the pump to be permanently installed inthe well is to be used for development, then it must be set above the screen in the casing to avoid beingdamaged by all the fine sand coming into the well. A bailer or sand pump will need to be used to removethe fine material and sand after the backwashing and overpumping.

High Velocity Water JettingHigh velocity water jetting should be performed simultaneously with air lift pumping. Theoutside diameter of the jetting tool should be 1 inch less than the screen inside diameter.The minimum exit velocity of the water should be 150 feet/second. The tool should berotated at a speed less than one rpm, should concentrate on one 4-5 inch area of the screenat a time, working over a 3 foot section of screen. Jetting should proceed from the bottom ofthe screen to the top, with pumping from the well occurring at 15-25 percent more than therate of jetting.

High velocity water jetting involves forcing water through the screen openings, agitating and rearrang-ing the formation materials. Water enters the screen openings at the jets and reenters the well above andbelow the jets carrying the fine materials into the well. Jetting is often combined with air lifting to thenremove the fines from the well. High velocity water jetting works most effectively on highly stratified,unconsolidated formations and consolidated bedrock formations such as sandstones. This system is one ofthe most successful methods that can be used for development with a continuous slot or wire wrappedscreen. It is 100% controllable and can be accurately used to ensure that the entire intake portion of thewell is developed.

A jetting tool is connected to the drill string, with the nozzles in the tool sized to suit the pressures andvolumes required for the application. The diameter of the tool must be correctly sized to the diameter ofthe screen used. The pumps and availability of water required must be taken into consideration. The highpressure water jets can be directed at all parts of the formation by rotating and raising and lowering thetool. A screen with the optimum open area must be used to allow the water jets to be able to reach all ofthe formation. This technique needs to be carefully controlled and caution must be used to avoid jetting fortoo long a period at a time. This will cause water to flow from inside the well to the outside, and will forceall of the fine material to remain in the formation. To avoid this, the well should be pumped at the sametime as the jetting is done. The pumping rate should be 15 to 25 percent higher than the injection rate usedfor jetting. Alternatively, the jetting could be done for a limited period of time, and then the well pumpedfor at least 30% longer than the jetting time used.

BailingBailing should be used to alternately create a pumping and backwashing action to effectivelydevelop the well. Initial development action should be gentle and increase to higher bailingspeeds as development proceeds. Fine materials must be removed periodically.

Bailing can be a reasonably effective system to use for low yield, small diameter, or shallow wells. Thebailer is used to alternately create a pumping and backwashing action, and then used to remove fines fromthe well. Initial bailing and surging should be slow, then increased with vigor to effectively create thetwo-way washing action. Fine material should be removed periodically from the well. The bailer size isvery important as it has to be able to remove a suitable amount of water on each stroke without becomingto heavy to operate for the equipment being used. The bailer must be sized to suit the diameter of thecasing and the screen. For telescopic screens, caution must be used when running the bailer into thesmaller diameter screen.

HyrofracturingHydraulic pressure applied rapidly in a focused fashion can be used to open existing frac-tures in low-yielding bedrock aquifers. Proper use of this method requires knowledge of thewell’s construction and experience with the type of lithology comprising the aquifer.

Hydrofracturing is accomplished by applying hydraulic pressure to a sealed zone in the well. Typi-cally, water is pumped into a well at pressures between 1000 and 3000 psi using a high-pressure pistonpump. The zone of interest is sealed by a packer assembly. Single or straddle packer assemblies can beused, although the single packer method is more common. The force of the injected water will open anypreexisting fractures in the bedrock, thus increasing yield to the well (ADITC, 1997).

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Chemical TechniquesChemical techniques are used in conjunction with the mechanical techniques to enhance the effective-

ness of the development process and to decrease the amount of time necessary for development. The mostcommon chemical additives for well development are dispersing agents and acids.

Dispersing AgentsNon-phosphorus-containing dispersing agents should be used only when necessary andshould be pre-mixed and used according to the manufacturer’s recommendations. Chlorineshould be added to the mix water to prevent bacterial growth.

By adding dispersing agents to the well or the jetting water, the clays and fine materials are brokendown and washed out of the formations and the gravel packs more easily than with plain water. Dispersingagents will break down the mud cakes on the wall of the well and increase the effectiveness of the devel-opment technique used. The most commonly used dispersing agents are polyphosphates. However, thephosphorus in these compounds attaches to the clays, and serves as nutrition for any biofouling microflorapresent. These phosphorus-containing compounds are usually not developed out sufficiently to avoidbiofouling. Instead, manufacturers have developed polyacrylamide and other non-phosphorus-containingdispersants to eliminate problems with biofouling (NGWA, 1998 and Mansuy, 1999).

Dispersing agents should be used only when absolutely necessary; typically, they are used for anextraordinarily bad interbedded clay situation, or because of poor drilling mud control. Chlorine is oftenadded to the water to minimize the occurrence of bacterial growth; yet in some cases, chlorination mayencourage bacterial growth by breaking down long-chain polymers and making phosphorus more avail-able as a nutrient (Smith, pers. comm., 1999).

These dispersing agents only work on contact with the clays and muds. The mechanical surging andjetting allows the dispersants to operate effectively. Excessive doses and high concentration mixes shouldnot be used. Dispersants should not be left in the well for prolonged periods of time without agitation andor mixing as the full benefit of the contact with the muds will not be achieved. Dispersants should not beused in formations that have thinly bedded clays and sands; the chemicals tend to make the clays unstablenear the borehole, causing mixing with the sand and reduction in the permeability of the formation.

AcidsAcids should be used as necessary and according to the manufacturer’s instructions. ProperpH must be maintained in the borehole to ensure the effective action of the acid.

The use of acids in certain formations, such as limestones, dolomites, and sandstones with calciumcarbonate-based cement, will often increase the effectiveness of well development due to their ability toremove carbonate. These acids should be high-quality (NSF-rated or equivalent) HCl, not muriatic grades.The treatment should be light; that is 15% or less in solution (Smith, pers. comm., 1999). Acids only workon contact; therefore, they should not be used until all clays have been removed during the initial cleaningwith the dispersing agents. Acids must be used with extreme caution; the fumes often are more lethal thanthe product itself. Proper ventilation is vital and protective clothing must be used. The pH must be moni-tored and maintained in the well to preserve the effectiveness of the acid. The acid solution must beneutralized before discharging from the well.

Well Testing

Testing For QuantityAfter a well is completed and developed, a test should be performed to determine the rate at which

water can be reliably produced. Simple tests that can be performed while the drilling rig is still over thewell are usually sufficient to estimate the capacity of a well drilled for domestic uses. For larger capacitysupplies, pumping tests should be conducted to determine (1) the performance characteristics of the welland (2) the hydraulic characteristics of the aquifer. The level of effort and degree of sophistication requiredfor these pumping tests should be based on the quantity of water that will be used and the resource poten-tial of the aquifer. In certain situations, more careful testing may be necessary regardless of the size of thesupply if the desired well capacity is at or near the limit of the reasonable expectation for thathydrogeologic setting.

Pumping test data, taken under controlled conditions, give a measure of the productive capacity of acompleted well and will provide information needed for the selection of pumping equipment. An accurate

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test of a well before the pump is selected pays for itself by assuring that the pump will perform efficientlyand reliably. Many times, unsatisfactory pump performance is due to an improperly selected pump ratherthan a problem with the well itself. Long term reliability of the system can be ensured when the perfor-mance characteristics of the pump are appropriately matched to the performance characteristics of thewell.

Another purpose of pumping tests is to provide data from which the principal factors that governaquifer performance can be determined. This type of test is called an aquifer test because it is primarily theaquifer characteristics that are being determined, even though the well performance characteristics canalso be calculated. Aquifer tests can be used to predict or estimate (1) the effect of new withdrawals onexisting wells, (2) the drawdown in a well at future times and at different pumping rates, (3) the radius ofthe cone of influence for individual or multiple wells, and (4) the amount of recharge potentially available.Aquifer tests are necessary for larger systems and where the dynamics of multiple wells and pumpingcenters add complexity to the hydrogeologic setting.

The pumping test method selected depends on the type and classification of well to be tested alongwith the type of information the tester wishes to obtain from the test. The purpose of this section is toprovide a classification for wells based on design capacity, and recommend pump test methods suitable fora particular classification of well.

Data from a pumping test should be thoroughly analyzed by a ground water professional prior todetermining the design pumping rate. Data from a pumping test using the step-drawdown tests and aquifertests should be analyzed by a professional hydrogeologist.

Guidelines For Quantity Testing RequirementsTwo types of pumping tests are used for potable water wells. Well tests are used to deter-mine the performance of a particular well. Step-drawdown pumping tests and constant ratepumping tests are the primary methods for evaluation of well performance. Aquifer tests areused to determine the hydraulic characteristics of the aquifer being tested. Selection of thetype of test conducted depends on the data one wishes to obtain from the test and the wellclassification being tested.

For the purpose of these guidelines, wells are classified into four types based on estimatedwell production in gallons per day. The classifications are very low use (domestic), low use,medium use and high use as indicated in the table below.

In developing a potable ground water supply system, the well driller or designer must consider both thecapacity of the proposed well and the user’s estimated water demand needs. Well capacity can be definedas the volume of water per unit time that can be discharged from a well without pumping the well dry ordamaging the aquifer. An estimate of the users average daily water demand needs can be determined usinghistorical usage data (meter readings), fixture counts, or calculation using information contained in Table1, found in Appendix III. Once the average daily water demand has been estimated, peak hourly demandcan be calculated using the following equation:

Average Daily Demand x 10 = Peak Hourly DemandPublic water systems utilizing a hydropneumatic pressure system must have sufficient well capacity to

meet peak hourly water demand. Failure to meet peak hourly demand with a single well may require eitheradditional wells to be developed, or installation of a water storage tank. Private (domestic) water systemsmust have sufficient capacity to meet the intended user’s water demand needs.

CLASSIFICATION AVERAGE DAILY USAGE (GPD)

Very low use (domestic) <1000

Low use 1000 to < 10,000

Medium use 10,000 to 100,000

High use >100,000

Table 2. Well Use Classification

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In most cases, if the well driller or designer thinks that the well capacity meets or exceeds the estimatedpeak hourly demand, a pumping test conducted at the peak hourly demand rate for a predeterminedduration would be sufficient. Unfortunately, many wells do not have sufficient capacity to sustain a peakhourly flow rate. These guidelines will establish criteria for pump testing wells that cannot sustain or arenot designed to meet peak hourly demands.

Very low use (domestic)For very low use (< 1000 GPD) domestic wells, well tests utilizing the bailing test method,the air blow test method, the air lift test method or the variable pumping rate method arerecommended.

Guidance for conducting these types of well tests will be discussed in the Simple Tests To EstimateWell Performance section of Appendix III.

The method selected should be based on the driller’s experience, equipment capability, site specificconditions, and accuracy required to make reliable judgements as to well yield and pump size needed. Insome circumstances it may be necessary to perform more elaborate pumping tests on domestic wells, ifmore precise data is required to determine a reliable well yield. Pumping tests on domestic and publicsupply wells are sometimes used to evaluate the capability of an area to support the development of asubdivision that will rely on individual wells. Pumping tests should be designed to reflect thehydrogeologic conditions of the area.

Low useFor low use wells ( 1000 to < 10,000 GPD), a well test utilizing the constant rate pumpingmethod is recommended.

A constant rate pump test can be conducted at the peak hourly demand rate (10 times the daily averagedemand). A constant rate pump test at this rate for the duration the well may be in operation would demon-strate that the well could sustain peak flows under all service conditions. In cases where the well cannotsustain peak hourly flow for the entire period of normal operation, the constant rate pump test should beconducted at 1.5 times the user’s needed design capacity for the duration the well may be in operation.Testing should be related to the well’s intended use.

For example:A high school with 500 students & 20 staff members wishes to drill a new well. The school is normally

open 12 hours per day. The existing system does not include a water meter, thus no historical data existsand the average daily demand must be estimated using Table 1 in Appendix III.

500 students @ 20 gpd/student 10,000 GPD20 staff members @ 20 gpd/staff + 400 GPD

= 10,400 GPD (7.2 gpm)Using equation 1, calculate the peak hourly demand: 7.2 gpm x 10 = 72 gpm

At this point, a step test with at least three steps can be used to extrapolate pumping levels at higherpumping rates. Or, it would also be possible to use the “variable pumping rate method” described inAppendix III. If the results from either test indicate that the proposed well can sustain the peak hourly rateof 72 gpm for 12 hours, this should be the minimum rate and duration that the constant rate pumping testis conducted. If the test results indicate that the well cannot sustain the peak hourly rate for 12 hours, adesign capacity for the well must determined, and the constant rate pumping test conducted for 12 hours at1.5 times the design capacity. The need for additional wells or water storage to meet the peak hourlydemand of 72 gpm must then be evaluated.

Medium useFor medium use wells (10,000 to 100,000 GPD), a well test utilizing the constant ratepumping method should be conducted for a minimum 24 hour period at 1.5 times the designwell capacity or at the estimated peak hourly demand rate, whichever is attainable in thewell driller or designer’s judgement.

A proposed well utilizing a hydropneumatic pressure system must meet the peak hourly demand unlessadditional wells or water storage is available. A step-drawdown pumping test should be utilized to collect

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additional information on well performance which can assist the well designer in determining optimumpumping rate and pump-setting depth. In complex hydrogeologic settings, pumping centers with multiplewells, and/or areas where desired capacity approaches the resource potential, aquifer tests should beconducted under the supervision of a professional hydrogeologist. Again, testing should be related to thedesign capacity of the well or its intended use.

High useFor high use wells (> 100,000 GPD), an aquifer test is recommended. As stated above,aquifer tests should be conducted under the supervision of a professional hydrogeologist.

A step-drawdown pumping test should be utilized to collect information on well performance andefficiency which can assist the well designer in determining optimum pumping rate and pump-settingdepth. Upon determination of a design well capacity from data obtained in the step-drawdown test, aconstant rate pump test at 1.5 times the design well capacity should be conducted for a minimum 24 hourperiod.

A more detailed discussion of the testing methodology recommended here can be found in Appendix III.

Testing For QualityPrivate water systems wellsPrivate water systems (domestic) wells should be sampled for total coliform bacteria as ageneral indicator of the presence or absence of bacteria in the system. When the well testspositive for total coliform after a minimum of 3 successive chlorination attempts, then thewell should be sampled and tested for e-coli. Wells should also be tested for nitrates. Incertain geologic formations across the state, naturally occurring constituents may bepresent, such as arsenic, barium, strontium, or radioactivity. If these constituents are knownor suspected to exist in the ground water, then wells should also be tested for their pres-ence. In areas of known man-made contamination, wells should be tested for volatileorganic compounds (VOC s) which may include BTEX (benzene, toluene, ethylene, xylene),semi-volatile organic compounds (SVOC s) or as deemed appropriate by the regulatingstate agency. At a minimum, homeowners should test their well(s) once a year for totalcoliform.

Raw water samples should be collected and analyzed after all traces of development and disinfectantchemicals have been completely flushed from the well and the plumbing system. If the well is beingsampled after alterations or rehabilitation on the well has been performed, it is critical that all mineralencrustation and bacterial slimes have been effectively removed from the well as they may provide asubstrate for coliform bacterial growth. The presence of nonpathogenic heterotrophic bacteria in thesubsurface that are attached to these substrates can contribute to total positive coliform results. After wellalteration or rehabilitation has been completed, the well should be completely flushed by pumping toremove at least 2-3 borehole volumes of water, or ideally, a pumping test could be performed.

Appendix IV describes correct procedures for water sample collection. If sample collection is made atthe tap, then chlorination of all plumbing, tanks, etc., must occur prior to sample collection. To sample thewater from the well only, the sample should be collected at a point in the line or system before it reachesthe pressure tank. At least 2-3 borehole volumes of water should be removed from the well prior tosampling to ensure that the water collected is coming from the aquifer.

If laboratory analysis of coliform bacteria test shows the raw water sample as unacceptable (coliformpositive), disinfection of the entire system should be performed and sampling should be repeated. If thesamples results are still coliform-positive, chlorination should be repeated and the subsequent samplecollected from the well at a point prior to the pressure tank to determine whether the source of contamina-tion is in the well or the plumbing system. Chlorinate the well and/or system again as necessary andcollect a subsequent sample. Contact the local health department to perform an investigation if three setsof unacceptable samples are obtained. If more than three unacceptable samples are obtained, then sam-pling for e-coli to determine speciation should be performed to help determine the source of contamina-tion. Assume a structural problem if total coliform positives persist. Look for indications of routes forcontamination to reach a well (e.g., a broken sewer cleanout near a swale where a well is completed inshallow bedrock). Conduct a borehole TV survey and repair problems if possible, or plug the well andredrill in a safe location.

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Other chemical constituents the intended water user may wish to have the well sampled for can includemineral content or hardness. Mineral content and hardness have little affect on the potability of water, buttheir removal from the potable water may be necessary for aesthetic and economic reasons. Depending onthe intended use of the well, the user may want other tests performed if specific water quality parametersare required.

Public water system wellsAll new potable water wells developed to serve a public water system must be sampled fortotal coliform bacteria and chemical parameters as required by the director of the Ohio EPA.

Contact the appropriate district office of the Ohio EPA, Division of Drinking and Ground Waters forsample collection procedures and a list of required analysis for new wells to be used by public watersupplies. All microbiological and chemical analyses conducted on a public water system water sourcemust be analyzed by a laboratory certified for such analysis by the Ohio EPA.

Chemical samplingCollection, preservation and analysis of any additional raw water samples should be conducted in

accordance with guidelines found in the latest edition of Standard Methods For the Examination of Waterand Wastewater. Contact an appropriate contracting laboratory for information and guidance.

Well CompletionThe proper completion of the well is as important as the proper construction. The well must be com-

pleted so that it is protected from surface contamination and physical damage. Well completion involvesthe finished height of the well casing above grade, the installation of a pitless device, vent pipe, and thewell cap. Physical protection for the exposed well casing should be a consideration in areas of high traffic.Installation of the pump and associated equipment is also part of the completion process, but it will not beaddressed in this guidance.

Pitless DevicesPitless devices, whetheradaptors or pre-assembledunits, should be installed byan experienced contractorbelow the frost line (typi-cally 32" below the groundsurface or greater, depend-ing on local conditions, oruse 48" if frost line isunknown). These devicesshould meet PAS97 Stan-dards established by theWater Systems Council.

Buried well seals and well pitinstallations are not consideredsatisfactory for adequatelyprotecting the well from contami-nation. A pitless device willprotect the well by allowing thepump to discharge through theside of the well casing whilepreventing the intrusion ofpotentially contaminated waterfrom the ground surface. Pitlessdevices must be installed when-ever the pump discharge pipingexits the casing below grade (seeFigure 14).

Figure 14. Example of pitless adapter installation.

Casing at least 8" above grade

Vented well cap

Drop pipe

32" orgreater

O-ring Pitless adaptor

Check valve

Submersible pumpCasing

Torque stop

Pressure line topressure tank

Electric cable to pump

Electric cable in conduit

Building foundation

Frost line

Gasket

Pitless Detail

O-ring

Gasket

Well Casing

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Pitless devices are constructed so that they seal tightly against the sides of the well casing. Therefore,the hole made in the casing for the installation of the pitless device should be cut with a hole saw or othertool capable of making a clean and uniform hole to allow proper sealing. A cutting torch is not recom-mended for creating the hole, as this method can easily lead to irregular or oversized holes that have roughsurfaces.

The pitless device must be installed below the frost line to protect from freezing. Frost line data can beobtained from county soil surveys, or, lacking that information, a minimum depth of 32-48 inches isrecommended as a working standard.

Non-pitless DevicesA pitless device may not be necessary if an above-ground discharge is used. Seals andvents should be used to provide physical protection from potential damage, adverse weatherconditions, and contamination. There should also be a convenient access to measure waterlevels.

In this situation, an above-ground well seal could be used in place of a pitless device and the well cap.Easy access for water level measurements should always be provided, especially if a steel plate is perma-nently welded to the top of the well casing.

Distribution LineAll plumbing materials used for the distribution line from the pitless adaptor to the pressuretank should be in compliance with AWWA or NSF standards.

Sample Tap or PortSample taps or ports should be installed prior to the pressure tank at a reasonable height tofacilitate the collection of water samples. No drainback frost-free hydrants should be usedfor this purpose. If an outside or wellhead tap is needed, use blowout type sampling hy-drants designed for this purpose.

Casing Termination and Surface CompletionThe casing height above finished grade should be a minimum of 12" for all wells, but local-ized conditions may necessitate the use of more casing if the well is located in an areaprone to flood events. For all wells, drainage away from the well casing is recommended.

The top of the casing at its finished height should be cut so that its surface will fit flush with the wellcap and properly seal the top of the casing. The portion of the casing that extends above the groundsurface must be of a size so that standard well caps will fit properly. Large diameter excavated wellsshould be finished with an impermeable surface seal sloping away from the well and extending beyond theedges of the excavation. Drive point wells should be fitted with a tee to facilitate access to the well.

Well CapsAll well caps/seals should form an insect-tight seal with the top of the casing to prevent entryof insects or other pests and meet the standards of PAS-97. Caps/seals should be securedwith screws or other appropriate hardware. Well caps used on wells located in floodplains orareas subject to flooding should form watertight seals with the casing.

Well caps should be secured to discourage unauthorized removal and the entry of insects and pests.Well caps should meet standards set by the Water Systems Council under PAS-97.

VentsAll types of wells should be vented. Vent piping should be self-draining and screened with anoncorroding, 24 mesh (.043") minimum size screen that prevents the entry of insects. Forwells located in a floodplain, the vent must extend 3' above the 100-year flood elevation.

Venting of all wells is essential to maintain equalized air pressure and prevent increased dissolved gasintroduction into the well. Vent pipes for wells in floodplains should be turned down and reinforced orattached to a stable object to reduce damage during flood events.

Physical ProtectionWell casing should be physically protected when the well is located in a high traffic area.

Physical protection for the well casing should be considered when a well is located where it may be subjectto damage. Damage to the exposed casing could allow surface contaminants to reach the aquifer. Barriers, such

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as guard posts or a well house, should be considered when a well is located near a high traffic area. The use ofconcrete pads is discouraged, unless the likelihood of cracking and heaving can be alleviated.

Super Chlorination (Shock Disinfection)A well should be chemically disinfected by calculating the amount and concentration ofchlorine necessary for complete disinfection based on well depth and volume of water in theborehole. Initial chlorine concentrations equivalent to 250 mg/l (or ppm) for new wells and500 mg/l for existing wells should be maintained for a minimum contact time of 8 hoursunless the pH of the water in the well is controlled. Always exercise caution when usingchlorine in its various forms; follow handling instructions on the label carefully. When usingbleach products, use only unscented varieties.

A properly constructed drilled well is regarded as the most sanitary type of private water system. Awell should be maintained in a sanitary manner through all stages of the construction process to protectpublic health and the ground water resource. All equipment should be cleaned and disinfected periodicallywhile the well is under construction and the well chemically disinfected upon completion. All equipmentand well construction materials should be kept off of the ground to prevent contamination by soil andpathogenic bacteria.

Sodium hypochlorite (liquid) or calcium hypochlorite (granular or pellet form) are readily availableproducts that can be used for the disinfection of wells. Concentrations of 500 mg/l are recommended fordisinfection of existing wells in Ohio due to the presence of bacterial slime, iron, manganese, totalorganic carbon, and variability in pH. A disinfectant solution of 250 mg/l is recommended for newwells. Actual chlorine concentrations will vary over the period of disinfection due to the presence ofthese constituents and variable water chemistry in the borehole. The addition of chlorine products to awell causes a rise in the pH of the water in the well. The biocidal activity of the chlorine is reduced withincreasing pH, with minimal biocidal capability at a pH equal to or greater than 9. Where pH levels aregreater than 8, a buffering agent or mild acid will need to be added to reduce pH levels from 6 to 7.5 toensure maximum effectiveness of the chlorine. Buffering agents can include mild acids such as acetic(vinegar), citric acid, or commercially available buffering solutions. When pH levels are controlled,chlorination contact time can be reduced to 30 minutes. Chlorine concentrations in the well may declineover time as the chlorine reacts with these constituents reducing the free available chlorine. Concentra-tions of 500 mg/l will also help ensure that proper disinfection will occur over the estimated contact timeeven if some of the chlorine reacts with other constituents in the well. Theoretically, the contact timeneeded to complete disinfection at this concentration should be only moments after contacting themicroorganism. However, since the chlorine must actually contact all microorganisms, the solutionshould remain in the well and plumbing for at least several hours to help ensure uniform dispersal of thechlorine solution and provide the greatest opportunity to kill all microorganisms.

The gallons of water to be disinfected should be determined by calculating the total amount of waterstored in the well and all related storage, or pressure tanks, existing plumbing and attached fixtures. Whencalcium hypochlorite is used for disinfection, the tablets or granules should be completely dissolved inwater prior to placement into the well. Sodium hypochlorite solutions should be used within themanufacturer’s posted expiration date. Sodium hypochlorite solutions with fragrance additives should notbe used for disinfection. Sodium hypochlorite and calcium hypochlorite should not be mixed with otherchemicals for disinfection purposes and all manufacturer’s directions must be followed.

An appropriate amount of disinfectant to make a 250 or 500 mg/l chlorine solution, as calculatedfrom Tables 2 and 3, should be placed into the well. Calcium hypochlorite should not be used on wellscompleted in limestone aquifers, or where the water has high levels of dissolved calcium due to theformation of calcium hydroxide or calcium carbonate precipitates in the well that may cause well yieldlosses. The water in the well should be agitated or surged to ensure even dispersal of the disinfectantthroughout the entire water column. Chlorinated water in the well should be recirculated to wash downthe sides of the well casing for a minimum of ten minutes. Chlorinated water should then be circulatedthrough the distribution system and the plumbing within the dwelling or building.

In some instances, where traditional disinfection methods do not appear to be sanitizing the watersystem, more stringent procedures can be employed. This may include the use of a surge block or jettingtool, or an inflatable packer to help force the chlorine solution back into the formation. The addition of aslug of chlorine solution 1 to 2 times the well bore volume into the well can also be performed to try to

36

force chlorinated water into the formation. Increasing the concentration above 1000 mg/l will not improvethe chances of sanitizing the well. The key to successful chlorination is to actually force the sterilant intocontact with all surfaces that need disinfection. In some older wells and water systems bacteria may beprotected by mineral scale and/or the formation of bacterial slime layers over their surfaces. Thesebacterial havens can be removed by agitation, physical surging, or the use of well rehabilitation acids todissolve and remove scale before disinfection. Any acids used to remove mineral scale or bacterial slimesmust be completely removed from the well prior to the addition of chlorine to prevent the development oftoxic gases.

The removal of protective bacterial slime layers has been a subject of much discussion. There is someindication that slime layer thickness may actually increase with increased chlorination. Therefore, thecasing may need some sort of scrubbing to physically remove the protective barrier prior to chlorinationtreatments. Old plumbing can present problems, especially where work has been done that leaves deadends that the chlorine cannot reach. In these cases, the dead ends in the plumbing system should beeliminated prior to another shock treatment.

After the appropriate amount of chlorine has been added to the well, and any mechanical procedures,such as agitation, surging, scrubbing, etc., have been performed, pump to waste until clear, then turn onall of the spigots in the building until chlorine is detected by smell and immediately shut off. The watersoftener should not be bypassed because the resin bed may be harboring microbiological growth. Thesoftener should receive the same disinfection treatment as the rest of the system, even though there is achance of slightly reducing the life of the resin bed. The chlorine solution is generally left in the well andplumbing for a minimum of 8 hours and no more than 24 hours and then disposed of properly. Chlorinatedwater from the well and plumbing should not be discharged to the septic system or local streams or riverswithout dechlorinization. It is better to wait until a few days after this process to take a water sample toallow time for the remaining chlorine to dissipate. The water should be tested for a chlorine residual justprior to sampling. A water sample should never be taken from a well if there is any chlorine residualremaining in the well.

Well MaintenanceEffective well maintenance requires the selection of well materials and design that will retardand/or prevent corrosion and biofouling, regular monitoring of well performance and waterquality as indicators of possible deterioration, good record keeping of well performance andmaintenance, and preventative treatments to prevent well deterioration in the early stages.Any chemicals or additives used for well maintenance should meet NSF Standard 61.

Well maintenance is a scheduled process of testing, inspection, repair and treatment to maintain wellperformance and water quality. Effective well maintenance will delay the need for extensive and expen-

Table 3. Volume of Water in Well

Diameter of Well (inches) Gallons per Foot of Water3 0.374 0.655 1.06 1.58 2.6

Table 4. Amount of Chlorine Added to 100 Gallons of Water for Disinfection

Chlorine concentration(parts per million or mg/l)

Gallons of 5.25% sodiumhypochlorite liquid bleach

Pounds of dry calciumhypochlorite

Minimumcontact time

500mg/l 1 gallons 0.75 pounds 8 hours

250mg/l 0.5 gallons 0.38 pounds 8 hours

37

sive well rehabilitation and may make rehabilitation unnecessary. Preventative maintenance will serve tolimit or retard well deterioration over time, and is more effective and less costly than well rehabilitationdue to crisis conditions.

Proper selection of well drilling and construction materials is necessary to minimize corrosion, othertypes of casing failure, or biofouling. Particular care should be made in the selection of steel casings,collars, fittings, and screens to prevent or minimize the development of galvanic corrosion due to contactbetween unlike metals. See NGWA (1998) for specific guidance in material selection.

Regular monitoring of well performance and water quality is essential to detect the early stages of welldeterioration. Well testing using continuous or variable rate tests are commonly performed after the well isdrilled. Information on the date of the test, test rate and duration, yield and drawdown should be carefullyrecorded on the well log and, if the test is more comprehensive, on appropriate pumping test forms.Benchmark step tests permit valid assessment of performance changes later in aquifer loss, well loss, andpump efficiency (Helweg et al., 1983, and Borch et al., 1993). Depending on the extent of the data col-lected, specific capacity and well efficiency can be calculated. Similar performance tests conducted atlater dates can be compared with the original values obtained after the well was first drilled. Modestvariations in these values can be an indicator of well deterioration. Significant deterioration (variationsgreater than 10 to 15%) indicate the need for aggressive well rehabilitation (Driscoll, 1986). Smallercapacity wells, such as domestic wells, should be tested at least once every several years, whereas largecapacity wells should be tested on a yearly basis or even more frequently (Gass, et al., 1980). Testing forwater quality should also be conducted on a relatively frequent basis depending on the well use. Waterquality testing on a regular basis will indicate contamination and the beginning stages of biofouling. Atotal coliform test is an indicator of the presence of contamination which suggests a pathway for contami-nants to enter a well. Total coliform tests will not detect the large majority of biofouling organisms. Theuse of a combination of available cultural (e.g. BART) and microscopy-based (e.g. Standard MethodsSection 9240) indicator tests must be used to detect biofouling. Microscopy alone is not sufficient. Smith(1992 and 1996) offers protocols for maintenance water quality testing. Chemical analysis for iron,manganese, pH, total organic carbon, total phosphorous, and nitrogen (as ammonia-N, nitrate-N andorganic-N) in addition to conductivity, and total dissolved solids can be used as important indicators thatconditions favor well deterioration (Smith, 1998).

Accurate records should be kept of all aspects of well construction, testing, maintenance and/or reha-bilitation. A well log and drilling report must be accurately and completely recorded for each well. Testingand maintenance results, dates, and the contractor who performed the work should also be carefullyrecorded and kept in a safe and accessible place. This information can be very critical when trying todiagnose future well problems.

Preventative well treatments should be applied on a regular schedule and consist of a lighter form oftreatment than is typically used for well rehabilitation. Where light biofouling has occurred, shock chlori-nation methods described in Appendix V of this document may be used. Chelating agents and organicacids may also be employed with surging and agitation to retard and/or remove more significantbiofouling and encrustation. Any maintenance and or rehabilitation techniques beyond simple chlorinationshould be performed by a qualified and knowledgeable well contractor.

Well AlterationsWell alterations can consist of changes made to the well above the ground surface or below. According

to the Ohio Department of Health’s Private Water Systems rules (Ohio Administrative Code Chapter 3701-28), an alteration “means a major change in the type of construction or configuration of a private watersystem, including but not limited to adding a disinfection or treatment device, converting a water well witha buried seal to a well with a pitless adapter or well house installation; extending a distribution system;converting a well using a well pit to a well with a pitless adapter or well house type of construction;extending the casing above ground; deepening a well; changing the type of pumping equipment when thatrequires making new holes or sealing or plugging existing holes in the casing or wall of a well; repairing,extending or replacing any portion or the inside or outside casing or wall, or of the walls of a spring orcistern that extend below ground level.” For the Ohio Department of Natural Resources, Division of Water(Ohio Revised Code Section 1521.05), altering any type of well defined in this section of the ORC “meanschanging the configuration of a well, including, without limitation, deepening a well, extending or replac-ing any portion of the inside or outside casing or wall of a well that extends below ground level, plugginga portion of a well back to a certain depth, and reaming out a well to enlarge its original diameter.”

38

Reporting RequirementsThe Ohio Department of Health requires that a permit be obtained for alterations prior to the start of

work, except in the case of emergencies. A completion form must be filed with the department within 15days of the completion of the alteration. Within 30 days of the completion of the alteration, a copy of thewell log and drilling report submitted to the Ohio Department of Natural Resources (ODNR) must befiled with the department. The ODNR, Division of Water requires that a well log and drilling report befiled within 30 days of the completion of any of the alterations described in its definition. The OhioEnvironmental Protection Agency requires that plans be submitted for any substantial change to a publicwater system and must be approved by the Director. Any public water supply system should contact theappropriate Ohio EPA district office regarding alterations to the system.

Above-Ground AlterationsAll couplings should be welded, threaded, or solvent welded to connect the existing wellcasing to the extension piece, and should form a watertight seal.

Above-ground alterations include casing extension to its required height above grade (12" minimum),addition or replacement of a pitless device, and installation of a surface seal for above-ground discharge.When extending the casing above grade, the mechanical coupling should not be used to connect theexisting well casing with the extension piece. Instead, the coupling should be welded, threaded, or solventwelded to provide structural integrity. The coupling should form a watertight seal between the two casings.Information on pitless devices and surface seals can be found in the section on Well Completion. After allalterations have been completed, the well should be disinfected using the procedures described in thesection on Well Disinfection.

Below-Ground AlterationsAll couplings, including mechanical, threaded, or welded, must maintain the structuralintegrity of the casing and/or liner and maintain a watertight seal. All liners must meet aminimum wall thickness of SDR 26 for PVC casing or ASTM A53, A589, or API Specification5L. All couplings, threads, or solvents must meet related ANSI/NSF, ASTM or API standards.For public water supply wells, all couplings should comply with the requirements of ANSI/AWWA Standard A100.

Below-ground alterations include deepening a well, plugging back a well, reaming out a well, addinga liner, or extending buried casing above ground. Liners should be watertight to a depth of 25 feet andmeet NSF Standard 61 or similar requirements. The minimum wall thickness of any liner installed shouldbe equivalent to SDR 26, and may need to be thicker, depending on its use. Typically, liners are usedeither to repair casing or to keep the borehole open in friable consolidated formations. A liner shouldextend to the bottom of the pitless adapter so that it will be visible from the ground surface. Whenextending buried casing above ground, couplings used should be welded, threaded, or solvent cementedto ensure structural integrity. Mechanical couplings can be used if they are able to maintain structuralintegrity and are suitable for pressure pipe applications. The coupling seal should be watertight. Forinformation on materials that should be used to plug back a well, refer to the State of Ohio TechnicalGuidance Document for Sealing Unused Wells, published in 1996. As mentioned above, once thealterations have been completed, the well should be disinfected before use.

Temporary Wells and Other Types of Subsurface InstallationsThe design of temporary wells and subsurface installations must be protective of the groundwater resources and prevent the infiltration of surface water and/or the mixing of water ofdifferent quality between multiple aquifers. Temporary wells and subsurface installationsshould follow the recommendations for well construction materials and installation proce-dures described previously in this document. Exceptions are described below.

A temporary well installation is a boring or well that is to be installed and used for less than one year.These typically include dewatering wells and a variety of test borings. Other types of subsurface structuresmay also be installed on a permanent basis that penetrate into aquifers but are not necessarily used forwithdrawing or recharging water. These include elevator shafts, cathodic protection wells, ground wells,and open and closed loop vertical geothermal wells. It is critical that these permanent structures be prop-erly designed and installed to prevent surface water contamination of aquifers, the leakage of oils or otherchemicals from these structures, and intermixing of different quality ground waters when multiple aquifers

39

are penetrated. Wells installed for temporary sampling or withdrawal of ground water must be properlyabandoned and sealed (for further information, refer to State of Ohio Technical Guidance Document forSealing Unused Wells, published in 1996). Key issues and exceptions to the recommended procedures aredescribed in the following discussions of each type of well and/or subsurface structure.

Dewatering WellsBecause dewatering wells are often used to withdraw shallow ground water for construction purposes,

grouting of the annular space can be minimized. Cuttings or clean gravel may be used to fill the annularspace to within 5 feet of the ground surface. A minimum of 5 feet of grout must be placed in the annularspace to the ground surface. Casing length required is dependent on the target zone to be dewatered, butcasing length should be no less than 5 feet. Where dewatering of deeper aquifers is required, casing andproper grouting through the vadose zone and any upper aquifers should be installed. Dewatering wellsshould be properly capped during use. Dewatering wells installed in unique geologic conditions describedpreviously in this document should follow the appropriate recommendations. These wells should beimmediately sealed using methods described in the State of Ohio Technical Guidance for Sealing UnusedWells after dewatering has ceased.

Test BoringsThe installation of test borings should follow procedures identified in ASTM Standards D1452-80

(1995), D2113-83 (1993), D6151-97, and D5784-95. Test borings should not penetrate multiple aquifersand allow the mixing of water between aquifers. If multiple aquifers are to be penetrated, then casing andgrouting should be installed and removed upon completion and sealing of the test boring. Test boringsinstalled in unique geologic conditions described previously in this document should follow the appropri-ate recommendations. Proper sealing of test wells must be performed either according to the State of OhioTechnical Guidance for Sealing Unused Wells or ASTM Standard D-5299.

Geothermal WellsThe installation of permanent open and closed loop vertical geothermal wells should follow the recom-

mended materials and installation procedures described previously in this document for water wells.Closed loop vertical geothermal wells should be grouted the entire length of the borehole and only non-toxic transfer fluids should be used.

Cathodic Protection and Ground WellsCathodic protection and ground wells should follow the recommended materials and installation procedures

described previously in this document for water wells. These wells should be properly cased and grouted. Thebottoms of these wells should be sealed to prevent the intrusion of ground water into the borehole where it couldcontact materials used to fill these wells. Any fill materials used should be nontoxic.

Elevator ShaftsElevator shafts should follow the recommended materials and installation procedures for water wells

described previously in this document. All casings, liners and joints should be water tight and properlygrouted. The bottom of the shaft must be properly sealed and should not serve as the drain for the pit.Shafts should not allow cross-contamination between aquifers. Double wall cylinder shaft installations arerecommended. If single wall cylinder shafts are installed, then the borehole should be cased to the bottomof the excavation. Shafts completed in bedrock may have two casings, a surface casing set into the rock,and an inner casing set to the bottom of the shaft. The annular space between these casings should begrouted according to recommendations described previously in this document. Protection from leakage ofhydraulic fluid can be achieved by either attaching a watertight cap or plate to the bottom of the casingand surrounding the casing with grout, by grouting the inside of the casing with at least two feet of neatcement or grout, or by encasing the cyclinder in a Schedule 30 plastic outer pipe or sleeve with the bottomof the pipe or sleeve capped and the top extending above the pit floor. The plastic casing is not structuralbut serves as a container to catch any leaked hydraulic fluids.

ConclusionsSince 1990, 143,385 well log and drilling reports were filed with the Department of Natural Resources,

Division of Water for domestic, irrigation, monitoring, municipal, and other water supply wells drilled inOhio. Consequently, an average of 15,932 potential conduits for ground water contamination have been

40

created each year during the 1990’s. Considering the fact that about 40% of Ohio’s population relies onground water for its drinking water (Ohio EPA, 1987), it is essential that all newly installed wells beproperly sited, constructed, developed, and tested to ensure the safety of our ground water resources. Toreach that goal, consistent state standards are needed. This guidance was developed to set those standardsin the form of recommendations.

The recommendations given in this document are general, and not intended to cover every conceivablecontingency. Rather, they should serve as a guide to handling unique situations when they arise. Geologicconditions vary across the state, and may dictate changes in recommended procedures. Any questions as tothe suitability of a particular procedure for certain conditions should be directed to the appropriate regula-tory agency.

These recommendations do not constitute a guarantee or any implied guarantee regarding the perfor-mance of any well that has been drilled, altered or rehabilitated according to the recommendations in thisdocument.

41

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Listing of American Society for Testing and Materials (ASTM) StandardsReferenced

A53 Standard Specification for Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, Welded andSeamless

A106 Standard Specification for Seamless Carbon Steel Pipe for High-Temperature Service.A500 Standard Specification for Cold-Formed Welded and Seamless Carbon Structural Tubing in

Rounds and ShapesA589 Standard Specification for Seamless and Welded Carbon Steel Water-Well PipeC150 Standard Specification for Portland CementC478 Standard Specification for Precast Reinforced Concrete Manhole SectionsC913 Standard Specification for Precast Concrete Water and Wastewater StructuresC990 Standard Specification for Joints for Concrete Pipe, Manholes, and Precast Box Sections using

Preformed Flexible Joint SealantsD1452 Standard Practice for Soil Investigation and Sampling by Auger BoringsD2113 Standard Practice for Diamond Core Drilling for Site InvestigationD5092 Standard Practice for Design and Installation of Ground Water Monitoring Wells in AquifersD5299 Standard Guide for Decommissioning of Ground Water Wells, Vadose Zone Monitoring

Devices, Boreholes, and Other Devices for Environmental ActivitiesD5784 Standard Guide for Use of Hollow-Stem Augers for Geoenvironmental Exploration and Soil

SamplingD6151 Standard Practice for Using Hollow-Stem Augers for Geotechnical Exploration and Soil

SamplingF480 Standard Specifications for Thermoplastic Well Casing Pipe and Couplings Made in Standard

Dimension Ratios (SDR) SCH40 and SCH80.

Listing of American Petroleum Institute (API) Standards ReferencedSpec 5L Line Pipe, Forty-First Edition, April 1, 1995RP 5B1 Threading, Gauging, and Thread Inspection of Casing, Tubing, and Line Pipe Threads, Fourth

Edition, December, 1996

Listing of National Sanitation Foundation (NSF) Standards ReferencedNSF Standard 14 Plastic Piping System Components and Related Materials, 10/28/96NSF Standard 61 Section 1 through 9 Drinking Water System Components, 9/25/97

Listing of Water Systems Council Standards ReferencedPAS-97 Performance Standards and Recommended Installation Procedures For Sanitary Water Well

Pitless Adaptors, Pitless Units, and Watertight Well Caps

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Glossary

Annular seal: an impermeable material placed between the outside of the casing and the borehole,or between two casings, to prevent movement of fluids from the surface or betweenformations.

Aquifer : a consolidated or unconsolidated geologic formation or series of formations thathave the ability to receive, store, or transmit water to wells or springs.

Artificial pack : filter pack materials placed directly around the screen.

Backwashing: the surging effect or reversal of water flow in a well during the development process.

Biofouling: biological growth in a well and/or the surrounding formation that interferes with theperformance of a well.

Borehole: a hole in the earth made by a drill; the uncased drill hole from the ground surface tothe bottom of the well.

Caliper log: simple logging device used to determine the diameter of a borehole, the presence ofsuch features as swelling clays or fractures in limestones or sandstones, and theamount of borehole erosion.

Casing: an impervious, durable pipe placed in a well to prevent the walls from caving and toseal off surface drainage or undesirable water, gas or other fluids, and prevent theirentering the well.

Chelating agents: substances that have the ability to sequester metal ions in solution and prevent themfrom combining chemically with other ions, used for well maintenance and rehabili-tation.

Cone of influence: the area, circular or elliptical in shape, in the ground water table or potentiometricsurface affected by a pumping well.

Confined aquifer: an aquifer bounded above and below by beds of distinctly lower permeability thanthat of the aquifer itself and which contains groundwater under pressure greater thanthat of the atmosphere.

Corrosion: the act or process of dissolving or wearing away metals.

Density: the mass or quantity of a substance per unit volume, usually expressed in grams percubic centimeter.

Dispersing agents: substances that have the ability to remove clays occurring naturally in the formation,and those introduced into the borehole as part of the drilling fluid, typically usedduring well development.

Drawdown: the distance between the static water level and the pumping level.

Effective grain size: the 90-percent-retained size of a sediment as determined from a grain-size analysis.

Entrance velocity: speed at which water moves into a well screen, should not exceed 0.1 ft/sec.

Filter pack : siliceous, well-rounded, clean, and uniform sand or gravel that is placed between theborehole wall and the well screen to prevent formation material from enteringthrough the screen.

Gravity emplacement: material installation by free-fall into desired position.

Ground water: any water below the surface of the earth in a zone of saturation.

Hydrated: the incorporation of water into the chemical composition of a mineral.

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Hydrogeologic setting: a mappable unit with common hydrogeologic characteristics.

Intake: screened or open borehole portion of a well that allows water to enter.

Leaching: removal of mineral salts by solution.

Mesh: one of the openings in a screen or sieve. The value of the mesh is usually given asthe number of openings per linear inch.

Microannulus: the space between the sealing material and the casing and/or the formation.

Mud balance: a scale that measures a specific volume of grout slurry (density) and is expressed inpounds per gallon.

Natural pack: created when the formation is allowed to collapse around the screen.

Plasticity: the capability of being deformed permanently without rupture.

Permeability: the property or capacity of porous rock, sediment, or soil for transmitting a fluid.

Porosity: the percentage of the bulk volume of a rock or soil that is occupied by interstices,whether isolated or connected.

Primary pack : part of an artificial pack, extends from the bottom of the borehole to the top of thescreen.

Private water system: any water system for the provision of water for human consumption, if such asystem has fewer than fifteen service connections and does not regularly serve anaverage of at least twenty-five individuals daily at least sixty days out of the year.

Public water system: a system for the provision to the public of piped water for human consumption, ifsuch a system has at least fifteen service connections or regularly serves an averageof at least twenty-five individuals daily at least sixty days out of the year.

Recharge: the processes by which water is absorbed and is added to the saturation zone, eitherdirectly into a formation, or indirectly by way of another formation.

Reverse circulation: any methodology involving injection of drilling fluid, water, or water/solids mixtureinto an annulus and returning it to the surface through the well casing or drill rod.

Screen: a machine-slotted or wire-wrapped portion of casing used to stabilize the sides of theborehole, prevent the movement of fine-grained material into the well, and allow themaximum amount of water to enter the well with a minimum of resistance.

Secondary pack: part of an artificial pack, placed directly on top of the primary pack to prevent theinfiltration of the annular seal into the primary pack.

Specific capacity: a measure of the productivity of a well, typically expressed by dividing the rate ofdischarge (usually gallons per minute) by the drawdown (usually in feet).

Strength: the limiting stress that a solid can withstand without failing by rupture or continuousplastic flow.

Surface protection: protective casing and surface seal used to safeguard well casing against physicaldamage and surface water infiltration.

Temporary well a boring or well that is to be installed and used for less than one yearinstallation:

Tremie pipe: small diameter plastic or metal tubing used to emplace sealants or filter pack materi-als.

Unconsolidated consists of rock and mineral fragments that have been deposited in layers but are not formation : cemented or are only partially cemented together.

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Uniformity coefficient: a measure of how well or poorly sorted a sediment is, expressed as the ratio of thesieve size on which 40 % of the material is retained to the sieve size on which 90%of the material is retained.

Viscosity: the property of a fluid or semi-liquid to offer internal resistance to flow.

Well: any excavation, regardless of design or method of construction, created for any ofthe following purposes: 1) removing ground water from or recharging water into anaquifer, excluding subsurface drainage systems installed to enhance agricultural cropproduction or urban or suburban landscape management or to control seepage indams, dikes or levees; 2) determining the quantity, quality, level, or movement ofground water in or the stratigraphy of an aquifer; and 3) removing or exchangingheat from ground water, excluding horizontal trenches that are installed for watersource heat pump systems.

Well efficiency: the ratio of actual drawdown in a well versus theoretical drawdown, usually ex-pressed as a percentage.

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Appendix IWell Drilling Methods Used in Ohio

There are three commonly used methods of well construction in Ohio: digging (by hand or backhoe),driving and drilling. Dug wells can be defined as any wells not installed by drilling rigs. They are usuallylarge diameter (greater than 24 inches) and fairly shallow (25 feet or less), and are constructed by diggingwith a backhoe or by hand. Casing installed in dug wells can vary from concrete pipe and vitrified tile tocobbles and bricks. In some cases, dug wells are improperly used as cisterns for roof runoff or hauledwater.

Driven wells, for the purposes of this document, will refer to well points exclusively. Well points areinstalled only in unconsolidated formations. Well points are typically small diameter, shallow wells usedto supply water for a single household. Many of these wells are installed by the homeowners themselves.Well points consist of a well screen with a hardened point on the end of the screen which is hammered intoplace (by hand or machine) using a large weight. Sections of pipe are added to the screen in order toadvance the screen to the desired depth.

The third major category of well construction methods is that of drilled wells. Drilled wells are thosethat are constructed using machines designed for specifically for the task of well installation. There areseveral drilling methods commonly used today: boring, cable tool, rotary, and vibratory drilling.

Bored wells are also known as augered wells and are used to construct wells in unconsolidated forma-tions. There are three principal types of augers used for well drilling: bucket augers, solid-stem augers,and hollow-stem augers. The bucket auger has the largest diameter of the three types of augers, and is themost frequently used augering technique for water supply wells in Ohio. The bucket is cylindrical withhardened teeth on the bottom and has a diameter of 18" to 48". The bucket can remove 24" to 48" ofmaterial at a time. Wells drilled with a bucket auger normally range in depth from 50 to 150 feet, but insome areas they can reach 250 feet in depth (Driscoll, 1986). In Ohio, a bucket-augered well could becased with concrete pipe or vitrified tile, and in many respects will resemble a dug well.

Solid-stem augers consist of spiral flanges welded to a pipe. One length of pipe (or auger section) iscalled a flight; multiple auger sections are often referred to as continuous flighting. The leading augerflight has a special bit or cutter head attached that cuts a hole for the flights to follow. Flights are added asthe hole is drilled deeper. Cuttings from the drilling process are brought to the surface by the action of theaugers (Driscoll, 1986). Boreholes constructed with solid-stem augers are typically used for geotechnical,or, less commonly, environmental purposes, rather than water supply wells.

Hollow-stem augers are similar stem augers in design, except that drill rods can pass through the augersections. The leading drill rod has a pilot assembly attached to drill slightly ahead of the lead auger flight.The outside diameter of these augers can range from 4 1/4" to 18", with corresponding inside diameters of2 1/4" to 12 1/4". Because the flights are hollow, they can be used a temporary casing to hold the holeopen while the permanent casing is installed. As the well is being installed, the augers are removed. Wellsdrilled with hollow stem augers have been used to construct water supply wells, but they are more oftenused to construct monitoring wells.

Cable tool (sometimes called “spudder”) rigs operate by repeatedly lifting and dropping a string of drilltools into the hole. The drill bit at the bottom of the drill tools breaks or crushes the formation and whenmixed with water forms a slurry. After drilling a certain number of feet, the bit and tools are pulled fromthe hole and the slurry is removed by bailing. In unconsolidated formations, casing is driven into thehole behind the drill bit so the hole will remain open. When the desired depth has been reached, the casingcan be pulled back to expose a screen, if one is to be installed. Otherwise, the casing is driven until a solidrock formation is encountered, and the casing is set a few feet into the bedrock. Cable tool drilling is stillthe most commonly used method of drilling water wells in Ohio. About 79 percent of the drilling contrac-tors operating in Ohio own cable tool rigs.

Rotary rigs use one of two methods to rotate the drill bit: a table drive or top head drive. The rotationof the table or top head is transferred to the drill rods, which in turn rotate the bit. Mud rotary rigs use aroller cone bit at the end of the drill rods. The drill cuttings are circulated out of the hole with water ordrilling mud. When the appropriate depth has been reached, the drill rods are withdrawn from the hole.The casing and screen (if needed) can then be set in the open borehole. Since it is necessary to drill anoversized borehole with this type of drilling method, the outside diameter of the well casing should be at

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least 2" smaller than the diameter of the borehole. Therefore, it is important that the space between thecasing and borehole wall (annular space) be sealed to prevent contamination from the surface, and to holdthe casing in place in the borehole.

Air rotary drilling rigs operate in basically the same way as mud rotary. However, instead of usingdrilling mud to clean the cuttings out of the borehole, a combination of compressed air and water is used.Air rotary rigs also run roller cone bits, but, in addition, they have the capability to run a down-the-holehammer. The down-the-hole hammer is used for consolidated formations only. Compressed air is forceddown the drill rods to operate the piston-like action of the hammer (bit). The hammer pulverizes thematerial being drilled through. The air, in combination with water or foam, lifts the cuttings out of thehole. Hole sizes can range from 4 1/8" to 30" (Ingersoll-Rand Co., 1988). Usually a well will be drilledwith mud through the unconsolidated formations to the bedrock formation, if that is the aquifer. After thecasing is set and grouted into place, the well can continue to be drilled with a combination of air and wateruntil the desired depth is reached. Both methods of rotary drilling are frequently used in Ohio to constructwater supply wells.

Another method of rotary drilling is reverse rotary. Reverse rotary drilling is most often used to con-struct large diameter (24 inches or greater) water supply wells. Reverse rotary rigs are similar to air ormud rotaries in design, but are larger in size. The bit is rotated by table drive exclusively, as the top headdrive does not develop enough torque to turn the size of the bit required to drill large diameter wells. Themajor difference between the reverse rotary and the other rotary methods described here is the pattern offluid circulation. With reverse rotary, the drilling fluid is added to the borehole through the annular space,then the fluid and cuttings are removed from the hole by suction up through the drill rods. The fluid andcuttings are deposited into a mud pit, where the cuttings settle out and the fluid is recirculated. The result-ing large diameter borehole allows easy installation of filter pack and well screens, which are necessary toproperly develop high capacity wells in unconsolidated formations. Reverse rotary drilling can also beused in most consolidated formations (Driscoll, 1986).

Vibratory drilling involves the use of a resonance source through the drill rods to drill a hole to thedesired depth. The resonance through the casing (rods in this case) pushes the cuttings into the side wall ofthe hole and into the center of the pipe. This method produces a minimal amount of cuttings, uses nodrilling mud, and produces a continuous core. This drilling method is used mostly for geotechnical andenvironmental sampling purposes. Monitoring wells can be set through the casing if desired.

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Appendix IIGrouting Materials

The data in this section relies heavily on information found in the Michigan Water Well GroutingManual (Gaber and Fisher, 1988).

Materials used for sealing the annular space around a well casing must have certain properties to makethem desirable for use. The ideal grout should 1) be of low permeability in order to resist flow throughthem, 2) be capable of bonding to both the well casing and borehole wall to provide a tight seal, 3) bechemically inert or nonreactive with formation materials or constituents of the ground water with whichthe grout may come in contact, 4) be easily mixed, 5) be of a consistency that will allow the grout to bepumped and remain in a pumpable state for an adequate period of time, 6) be capable of placement intothe well through a one inch diameter pipe, 7) be self-leveling in the well, 8) have minimal penetration intopermeable zones, 9) be capable of being easily cleaned from mixing and pumping equipment, 10) bereadily available at a reasonable cost, and 11) be safe to handle.

Grouting materials currently used in water wells are comprised of either cement or bentonite. Al-though there are advantages and disadvantages with each material and none of the grout materials avail-able today exhibit all of the desirable characteristics listed above, field experience has shown each to besuitable under most geological conditions. Table 1 lists advantages and disadvantages of cement andbentonite grouts.

Final permeability of the grout is recommended to be 1 x 10-7 centimeters per second to retard fluidmovement. Table 2 shows approximate permeability values for various sealing materials.

Cement-Based Grouts

Cement PropertiesPortland cement is the main ingredient in cement-based grouts such as neat cement or concrete. Ce-

ment is a mixture of lime, iron, silica, alumina, and magnesia components. The raw materials are com-bined and heated to produce cement clinker. The clinker is ground up and mixed with a small amount ofgypsum or anhydride to control setting time.

When Portland cement is mixed with water (producing neat cement), several chemical reactions occur.Heat is generated as the mixture cures and changes from a slurry to a solid. This is referred to as the heatof hydration and results in a temperature increase in the formation material at the cement/borehole inter-face and the well casing (Troxell, et.al., 1968; Portland Cement Association, 1979). The amount of heatgiven off is dependent upon several factors such as cement composition, use of additives, and surroundingtemperatures. Excessive heat of hydration may adversely affect the structural properties of PVC plasticwell casing (Molz and Kurt, 1979; Johnson et.al., 1980).

The setting of cement is controlled by temperature, pressure, water loss, water quality, and other factors(Smith, 1976). Warm water used for slurry preparation and warmer air temperature will cause fastersetting than cold water and cooler air temperature. Cement in the borehole will tend to set faster at thebottom since the weight of the cement column will increase hydrostatic pressure on the cement at thebottom. Water expelled from the cement into permeable zones will also result in an increased rate ofsetting. Standard Portland cement will reach its initial set in about 4 hours at a 50 F curing temperature.Table 3 shows total curing times for various cement grouts.

Cement TypesSeveral types of cement are manufactured to accommodate various chemical and physical conditions

which may be encountered. The American Society for Testing and Materials (ASTM) Specifications C150(ASTM, 1992) is the standard used by cement manufacturers.

Portland cement Types I and IA are readily available throughout Ohio. Type II cement is available atsome of the larger building supply outlets. Other cements are available by special order through cementsuppliers. The different types of cement and their appropriate usage are described as follows:

Type I - General purpose cement suitable where special properties are not required.Type II - Moderate sulfate resistance. Lower heat of hydration than Type I. Recommended for use

where sulfate levels in ground water are between 150 and 1500 ppm.

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Advantages Disadvantages

Table 1. Grout Properties

CEMENT-BASED GROUTS

BENTONITE-BASEDGROUTS

Suitable Permeability

Supports Casing

Shrinkage & Settling

Long Curing Time

Hard-Positive Seal High Density Results in Loss To Formations

Easily Mixed & Pumped

Heat of HydrationSuitable For Most Formations Affects Water Quality

Proven Effective Over DecadesOf Field Use

Properties Can Be AlteredWith Additives

Casing Cannot Be Moved After Grouting

Equipment Clean-Up Essential

Suitable Permeability With HighSolids Grouts

No Heat of Hydration

Premature Swelling And High ViscosityCan Result in Difficult Pumping

Difficult Mixing

Hard-Positive Seal High Density Results in Loss To Formations

Non-Shrinking & Self-Healing

Subject to Wash Out in Fractured Bedrock

Low Density Subject to Failure FromContaminated Water

No Curing Time Required

Casing Movable After Grouting

Equipment Clean-Up Difficult

Usage Instructions Vary For Each Product

(From American Colloid Co, and N.L. Baroid/N.L. Industries, 1989)

Sealing Material Permeability (K) in cm/sec

Table 2. Permeability of Various Sealing Materials

Neat Cement (5.2 gal water - 6 gal water maximum/94 lb sack) 10 -7

Bentonite Grout (20% Bentonite) 10 -8

Bentonite Pellets 10 -8

Granular Bentonite 10 -7

Granular Bentonite/Polymer Slurry (15% Bentonite) 10 -8

Coarse Grade Bentonite 10 -8

Grout Type Curing Time

Table 3. Cement Curing Time Required

Neat Cement - Type I 48 HoursConcrete Grout - Type I 48 HoursNeat Cement w/2% CaCl

224 Hours

Hi-Early Cement - Type III 12 HoursConcrete Grout - Type III 12 Hours

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Type III - High-early-strength. Ground to finer particle size which increases surface area and providesfaster curing rate (approximately 1/4 of the time it takes for Type I to cure). When Type IIIcement is used, the water to cement ratio must be increased to 6.3 to 7 gallons of water persack.

Type IV - Low heat of hydration cement designed for applications where the rate and amount of heatgenerated by the cement must be kept to a minimum. Develops strength at a slower rate thanType I.

Type V - Sulfate-resistant cement for use where ground water has a high sulfate content. Recom-mended for use where sulfate levels in ground water exceed 1500 ppm.

Expansive-type cements are also available in Ohio. This type of cement will expand upon curing byuse of additives in the mix, such as gypsum or aluminum powder.

Neat Cement GroutNeat cement slurry is comprised of Portland cement and fresh water, with no aggregate present. It was

first used as a grouting material in Texas and Oklahoma oil fields in the early 1900’s (Smith, 1976). Neatcement has since been used extensively in both the oil & gas and water well industries. Field experiencehas shown it to be effective for sealing off formations when properly applied. It can be mixed using awide variety of methods. Generally, lower pressures are developed while pumping neat cement grouts.The main disadvantages of using neat cement are shrinkage upon curing, possible formation of amicroannulus around the casing, and, in some cases, mixing according to manufacturer’s specifications,which can result in a thick mixture that is difficult to pump.

In some states, neat cement is considered superior to bentonite-based grouts in situations where bed-rock is encountered within 25 feet of ground surface. This is because it will form a hard, rock-like sealconsistent with the bedrock and will not wash out or dilute from higher ground water flow rates encoun-tered in some highly fractured formations.

The amount of shrinkage or settling, and compressive strength, of neat cement is dependent upon theproportion of water to cement in the slurry (Coleman and Corrigan, 1941; Halliburton Services, 1981). Asthe water to cement ratio increases, the compressive strength of the neat cement will decrease and shrink-age will increase. Laboratory studies and field experience have demonstrated that settling of cementparticles will occur, resulting in a drop in the grout level (Coleman and Corrigan, 1941, Kurt, 1983). Thetop of the hardened neat cement grout mass will generally be a few feet below the slurry level due to thissettling. Field observations show that the amount of settling will usually be 5 to 10 percent of the totalgrouted depth if the neat cement is mixed at 5 to 6 gallons of water per sack.

The American Petroleum Institute (API) recommends a water to cement ratio of 0.46 by weight or 5.2gallons of water per 94-lb sack of cement. This is the amount of water needed to hydrate the cement.More than 5.2 gallons/sack ratio will thin the grout and make it easier to pump, but will adversely affectthe grout’s sealing properties. This guideline recommends that the maximum amount of water mixed persack of cement be 6 gallons. The neat cement slurry at 6 gallons of water per sack of cement shouldweigh a minimum of 15 lbs/gal before pumping. At weights greater than 16 lbs/gal, pumping of the slurrybecomes difficult due to higher viscosity and pumping pressure. Density measurements of the slurryusing a mud balance are recommended to assure proper water-to-cement ratios.

Under certain conditions it may be necessary for the consulting engineer or regulatory agency tospecify an increase in the water to cement ratio. Factors such as the cement type, addition of additives,and quality of ground water will affect the grout performance and should be considered when planning thegrouting operation.

Concrete GroutConcrete grout consists of Portland cement, sand, and water. The addition of sand to a neat cement

slurry results in less shrinkage and tighter bonding to the casing and borehole. Also, the sand in the slurrywill aid in bridging pores in permeable formations. Concrete grout should be used only under specificcircumstances, such as for sealing the annular space in flowing wells, wells with natural gas or methanepresent, and wells with cavernous zones. Concrete should be handled only by experienced registereddrilling contractors due to the exacting requirements for its successful installation. Concrete grout must bepumped down a tremie pipe, or, if the borehole is free of water, poured down. Placing concrete groutthrough a column of water will cause the separation of sand from the slurry and result in placement

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problems. If concrete grout is used on a routine basis, it should be pumped through a metallic grout pipebecause it is highly abrasive on plastic pipe. Concrete grout can also cause excessive pump wear.

Other Cement AdditivesAccelerators may be added to cement to decrease its setting time when attempting to cement off flows

in and around casings. This will allow the cement to set before it is washed out of the hole. Calciumchloride is the most common and readily available accelerator. It is generally used at between 2 and 4percent by weight of cement. Accelerators should be used with caution since miscalculations or equip-ment breakdown can result in a cemented grout pump or hose. Other additives, such as retarders, weight-reducing agents, weighting agents, lost circulation control agents, and water reducing agents, are availablefor cements.

Bentonite-Based Grouts

Clay PropertiesClays are the principal ingredient of all bentonite-based grouts and drilling muds. They may be

characterized as naturally occurring substances which exhibit colloidal-like properties (remain in suspen-sion in water for a long period of time) and varying degrees of plasticity when wet (Bates, 1969). Theterm clay is frequently applied to a variety of fine-grained materials including clays, shales, and clayeysoils. They are all composed of small crystalline particles which are known as the clay minerals.

The common characteristic associated with clays is the very small particle size that has a very highsurface area to mass ratio. Negative electrical charges on the particle surface result in the interaction ofclays with other particles and water. This, coupled with the ability of certain clays to swell many timestheir original volume when hydrated, accounts for many of the properties and uses for clays.

The variety of bentonite commonly used in grouting materials and drilling muds is one in which theclay mineral is predominantly sodium-rich montmorillonite. Mined at relatively few locations, the major-ity of the high-grade sodium bentonite is obtained in Wyoming, Montana, and South Dakota (Gray andDarley, 1981). These clays are characterized by their ability to absorb large quantities of water and swell10 to 12 times in volume. Bentonite particles tend to remain in suspension an indefinite period of timewhen placed in water. The resulting slurry is of low density and high viscosity. Bentonites that havecalcium as the predominant exchangeable ion are less desirable as sealing materials because they havesignificantly lower swelling ability (Gaber and Fisher, 1988). That is why mixing cement and bentonite isineffective for preventing shrinkage of cement as it cures. Calcium ions in the cement replace sodium ionsin the bentonite by a process called ion exchange. The resulting calcium bentonite has little or no swellingcapability, and is therefore unable to prevent shrinkage of the cement (Smith, 1994).

Properties of Bentonite/Water SlurriesThree important physical properties of a water/bentonite slurry are: 1) density, 2) viscosity, and 3) gel

strength. A review of these properties will aid in understanding what makes a good bentonite grout.Density is defined as the weight per unit volume of a fluid and is commonly expressed in pounds per

gallon. The terms weight and density, although technically distinct, are frequently used interchangeably inthe drilling industry. The density of grout determines how much pressure is exerted on the formationwhen the fluid is at rest and is a direct indicator of the amount of clay solids present. The higher thedensity, the more solids are suspended in solution. Density is measured using a mud balance. A mudbalance measures a specific volume of grout slurry in pounds per gallon. The densities of various sealingmaterials can be seen in Table 4.

Measurements should be taken after each grout batch is mixed and a grout sample should also becollected after the grout appears at the surface. The grout discharged from the well should have a densityequal to that of the grout before it was pumped. The grout must be pumped into the well until dilution isminimal.

Viscosity is a measure of a fluid’s resistance to flow. The higher the viscosity of a fluid, the moredifficult it becomes to pump. The viscosity of bentonite-based grouts is dependent upon a number offactors including: 1) the density, 2) the size and shape of the clay particles, and 3) the charge interactionbetween the particles (Driscoll, 1986). Viscosity can be measured with a Marsh funnel viscometer, whichdetermines the time it takes to dispense one quart of fluid through the funnel. Water has a Marsh funnelviscosity of approximately 26 seconds; bentonite-based grouts should have a 70 second viscosity. Grout

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should be periodically checked for adequate viscosity. A low viscosity grout will make a less effectiveseal than a grout with the proper viscosity.

Gel strength is a measure of internal structural strength. It is an indication of a fluid’s ability to supportsuspended particles when the fluid is at rest. Gel strength is caused by the physical alignment of positiveand negative charges on the surface of the clay particles in solution. Gel strength is responsible for thequasi-solid (plastic) form of a clay/water mixture.

The gel strength is affected by how well the clay particles are dispersed in solution and the amount ofwater the particles have absorbed. Gel strength is not typically measured in the field. However, it isrelated to the fluid density and is dependent largely on the quality of the bentonite.

High-Solids Bentonite GroutBentonite products developed specifically for well grouting are widely available. Some use chemical

additives when mixing to control the development of viscosity and gel strength. By design, these productsare meant to be easy to pump, place, and clean up. Premature swelling and/or high viscosities may makethem difficult to pump when they are not mixed properly. Generally, bentonite grouts require higherpumping pressures than neat cement grouts (Gaber and Fisher, 1988). It also is important to know theenvironment into which the bentonite will be placed. For example, high concentrations of chlorides in thewater will suppress the hydration of bentonite unless it has been mixed with an agent that counteracts theeffect of the chlorides (Smith, 1994).

The bentonite-based grouts currently available can be broadly grouped into four classifications. Theclassifications reflect the degree of processing and the particle size of the bentonite constituent. The fourclasses of materials are: 1) powdered bentonite, 2) granular bentonite, 3) coarse grade bentonite, and 4)pelletized bentonite. Each class of bentonite requires a different handling and placement method. Manu-facturers recommend that mixing and placement methods should be assessed with regard to the depth tothe water table, the required depth of grouting, and other pertinent geological information.

Powdered Bentonite/Clay GroutPowdered bentonite/clay products available are similar in texture, appearance, and packaging to the

high yield drilling mud grade bentonite. They are a mixture of bentonite clays (sodium and calcium) andother clays and do not possess the expansion characteristics of grouts containing predominantly sodiumbentonite. They are marked as high solids clay grout with a resulting slurry of 15 to 20 percent clay solidsby weight of water and are designed to have extended workability. When properly applied, they result in aflexible seal of low permeability. Adequate mixing of this product requires the use of a venturi-type mixerand a mud rotary type mud pump and recirculation system or a paddle mixer.

(*From Halliburton Services, 1981)

Table 4. Grout Slurry Densities

Neat Cement 6.0 gal./sack of cement 15.0 1.28*5.2 gal.recommended/sack of cement 15.6 1.18*

Neat Cement& 6.0 gal./sack of cement 15.0 1.28CaCl (accelerator) CaCl - 2 to 4 lbs. sack of cement

Concrete Grout 1 sack of cement and an equal volume 17.5 2.0of sand per 6 gallon maximum water

Bentonite Benseal - 1.5 pounds/gallon of water 9.25 4.75Benseal/EZ-Mud EZ-Mud - 1 quart/100 gallons of water

Volclay 2.1 pounds/gallon of water 9.4 3.6

Minimum VolumeProduct Water Ratio Density ft3/sack

lbs/gal

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Some products utilize an inorganic chemical additive (magnesium oxide) referred to as an initiator, toaid in the development of gel strength. Exclusion of the initiator can result in decreased set strength,affecting the quality of the seal. Failure to meet manufacturer’s density requirements or placement of thegrout on top of a lower density material (e.g., drilling mud or water) can result in a disappearance of thegrout material from the well. This is due to a lack of gel strength development, resulting in settling ofbentonite material in the well or loss to surrounding formations. For this reason, the use of these productsrequires placement of the material the entire length of the borehole. A bentonite pellet or neat cement capa few feet thick is also recommended near the surface.

Granular BentoniteGranular bentonites are generally manufactured from high-yield, non-drilling grade sodium bentonite.

The bentonite is processed to provide coarse granular particles (predominantly 8 to 20 mesh) whichpossess considerably lower surface area-to-mass ratios than the finely ground, powdered bentonite. Thisresults in slower water absorption and delayed hydration and expansion when compared to a finely groundbentonite.

Dry granular bentonite can be used to grout driven casing. Called the dry driven grout method, thegranular bentonite is poured around the top of the casing as it is driven. The vibrations from the drivingprocess, along with the couplings on the casing, cause the bentonite to follow the casing down into theground. The bentonite will then form a seal around the casing as it hydrates in place. (See pp. 56-57 formore information.)

Granular bentonite slurries are typically used to grout wells with significant annular space. One advan-tage of the granular bentonite slurry is that the delay in swelling of the bentonite particles for a shortperiod of time (15 minutes or less) allows preparation of a slurry possessing a lower viscosity. If mixingand pumping are done efficiently, the granular bentonite slurries allow placement of a high density groutin a low viscosity state. Expansion of the bentonite then occurs downhole. Granular bentonite may beprepared with 15 to 20 percent solids content by weight. This results in a set grout which exhibits excel-lent permeability and gel strength characteristics.

These products rely on the addition of a synthetic organic polyacrylamide polymer to suppress thehydration and delay swelling of the bentonite particles. The use of such products requires particularattention to the manufacturer’s mixing recommendations. One recommended mixing procedure requiresaddition of the polymer to water at a rate of 1 quart of polymer per 100 gallons of water prior to adding thegranular bentonite at 1-1/2 to 2 lbs. per gallon (Smith and Mason, 1985). Mixing requires the use of bladeor paddle-type mixers or grout mixers with recirculation. Centrifugal pumps are not recommended formixing or pumping granular bentonite slurries. Upon addition of the bentonite, pumping of the groutmaterial must be accomplished before swelling of the bentonite occurs. If expansion occurs prematurelythe slurry cannot be pumped and the batch is wasted.

Coarse Grade BentoniteCoarse grade bentonite, also referred to as crushed or chip bentonite, is processed by the manufacturer

to provide a large particle size and density. The bentonite particles are sized from 3/8 to 3/4 inch and areintended to fall without bridging through a column of water in a borehole. When placed properly, thecoarse grade bentonite provides a high density, flexible downhole seal of low permeability.

Due to the size of the coarse grade bentonites, care should be taken in their use. Since the materialcannot be pumped, placement of the material requires pouring from the surface. Placement may beaccompanied by tamping to insure that bridging has not occurred. The bentonite must be poured slowly,and the pouring rate should not exceed the manufacturer’s specifications.

Prior to using this material, it should be sieved through 1/4-inch mesh screen to remove fines whichhave accumulated in the bag during shipment. These fines, if not removed, will clump if they hit waterand increase chances of bridging. Water should be poured on top of any coarse grade bentonite above thewater table to induce swelling.

Pelletized BentoniteThe pelletized bentonite consists of 1/4 to 1/2-inch size, compressed bentonite pellets. As with coarse

grade bentonite, pelletized bentonite provides a dense and flexible seal. Pelletized bentonite can bepoured directly into the well through standing water. Precautions similar to those for the use of coarsegrade bentonite are required to avoid bridging. As with coarse grade bentonite, water should be poured ontop of any pelletized bentonite above the water table.

56

DIVISION OF WATEROH

IO D

EPARTMENT OF NATURAL RESO

UR

CE

S


Fact Sheet 93–19

Water used for drilling operations may spill onto the areawhere the dry grout is being placed. This makes the groutswell, creating a temporary seal at the surface. This iscorrected by shoveling off the thin top layer of the moist-ened grout and exposing the underlying dry grout. If thegrout bridges during driving operations and no longermoves down the annulus, it is necessary to pull the wellcasing back two or three feet. By pulling the well casingback, the bridging of the grout is eliminated, and drillingand driving procedures may continue.

Grout Material

The type of grouting material used directly affects thequality of the grout job. Bentonite is advantageous to usebecause it incorporates the most important properties of thevarious grouting materials available.

Two different kinds of bentonite are suggested for usewith this method. The most popular bentonite is thegranular form. Experience has shown this type of bentonitereadily fills the annulus with minimal bridging and block-ing. The average cost is $12.00 per 50 pound bag. The othertype of bentonite is the drilling mud type of bentonite thatcomes in a powdered form. This type of bentonite comesin 100-pound bags and has an average cost of $5.75 per 50pounds of material.

Powdered bentonite, however, tends to swell rapidlywhen exposed to water and thus placement may be re-stricted due to bridging and premature swelling. The onlyadvantage of using powdered bentonite rather than granu-lar bentonite is lower cost.

Cost

The cost of dry grouting while driving well casing mustalso be considered. The cost of grouting is contingent uponthe size of the well casing, type of grouting material usedand the geologic formations encountered. The average costof material to properly grout a 5+ inch well constructed inglacial till is 72 cents per foot. This cost is based on usinggranular bentonite grout and an application rate of 150pounds per 50 feet of hole.

Dry Driven Grout Method

Drilling contractors are genuinely concerned aboutmaintaining and preserving the quality of groundwater–our most valuable natural resource. Dry

grouting while driving casing for the construction of wellsusing a cable tool drilling rig is one way to protect ourwater supply. Although grouting casing while driving isnot new to the water well construction industry, its appli-cation should be more widespread, and for very goodreasons. Dry grouting while driving well casing requireslittle effort, yet it provides many benefits.

Resource Protection

The primary reason for grouting a driven well casing isthe same as for other types of well construction. Thedriving of the casing into the ground creates a “micro”annular space between the casing and the geologic mate-rial. By placing an impervious layer of material in theannulus (space between the casing and borehole), theprobability of surface water intruding the aquifer is mini-mized. When the annulus is properly sealed, water isrestricted from flowing from one aquifer to another. Propergrouting techniques result in the best well constructionpossible. This fact sheet, and others pertaining to wellconstruction, will help you learn how to protect everyone’sground water.

The methods used to grout and drive well casing mayvary, but the following procedures cover the basic tech-nique.

Techniques

Initially, a 3-foot-deep borehole should be drilled ap-proximately four to five inches wider than the drill pipebeing used. Next, the casing is placed into the boreholeand the annulus is filled with a dry grouting material. Asdrilling continues, the well casing is then driven into theground approximately 12 feet while grouting material iscontinually placed around the drill pipe at the surface. Thegrouting material simply moves down the annulus alongthe casing. As additional well casing is driven, eachcoupling drags and pulls the grout down along the exteriorof the casing filling the annulus.

57

I 11/23/93


Division of Water, Water Resources Section1939 Fountain Square

Columbus, OH 43224-1336

Voice: (614) 265-6740 Fax: (614) 265-6767E-mail: [email protected]

Web site: http://www.dnr.state.oh.us/odnr/water/

ORThe Ohio Department of HealthPrivate Water System Program

(614) 466–1390OR Your Local Health Department

Advantages

The cost of grouting driven well casing is minimal inrelation to the advantages. Most Ohioans express a con-cern for the quality of their ground water and are notreluctant to pay the additional expense when the benefits ofgrouting are explained to them.

Bentonite Seals

The most obvious benefit of grouting a well is that theprobability of surface water or any other substance enter-ing the aquifer is minimized. Grouting also helps preventcross-contamination or mixing between aquifers with dif-ferent water quality. There are other benefits to theconsumer and driller from using this grouting technique.

Bentonite Lubricates

Bentonite grout enables well casing to move more freelyin the hole. Well screen installation in a cable tool drilledwell requires that the well casing move freely so that thedriller can pull the casing up to expose the screen. By usingthe bentonite grout method it is easier to pull back the wellcasing. Bentonite also allows casing to be driven to greaterdepths and in significantly less time.

Bentonite Protects

Another benefit of using this grouting technique is theway in which the outside of the well casing is protectedfrom corrosion. By placing an inert material around the

casing, corrosive elements are kept from direct contactwith the casing, preventing break down of the molecularstructure of the well casing.

Dry grouting while driving well casing can help topreserve ground water resources and provide efficientconstruction. Current Health Department rules requiredry grouting of cable tool wells. We strongly urge alldrilling contractors to implement a grouting programdirected at preserving our most valuable natural re-source.

(Edited and reprinted from Drill Bits, Winter 1989, Brad Ulery author)

For more information on well construction methodsand other water related topics contact:

Grout

}1. Casing set in an oversized upper borehole

2. Dry granular bentonite grout poured along casing as driving begins & continues

3. Depression forms in grout pile around casing as couplings help pull grout down.

3 Feet

58

Appendix IIIWell Quantity Testing

Quantity Testing MethodologyTesting methodology encompasses many elements. Factors to be considered include water level

measurement procedures, type of flow rate measurement, simple preliminary tests for estimating wellyield, types of pumping tests to evaluate well performance, types of pumping tests to evaluate aquifercharacteristics, and data collection and record-keeping. The first factor discussed here will be water levelmeasurement procedures.

The accuracy and reliability of data obtained from a pumping test depends largely on the accuracy ofmeasurements taken before and during the test. The method of measuring water levels in the well anddischarge rates while conducting the pumping test is often determined by the type of data the drillerwishes to obtain. This section identifies some common measurement devices used in the well drillingindustry with some of the advantages and disadvantages of each device.

Electrical tape methodThe electrical tape method utilizes an electrode suspended by insulated wires connected to an ammeter,

electric sounder, or indicator light. When the electrode touches the water surface, the ammeter or indicatorlight indicates a closed circuit. Depth to water level is determined by reading the calibrations on theinsulated wires. Care must be taken to ensure that depth markers not printed on the tape do not slip ormove on the tape. The accuracy of electric tapes should be checked periodically with a calibrated steeltape to insure the tape has not stretched, kinked, or that markers are accurate.

A primary advantage of this method is that, unlike the wetted tape method, the electrical tape does notrequire complete withdrawal each time a measurement is taken. Disadvantages include inaccurate readingsresulting from wet well casings and kinks or nicks in the insulated wire. Where cascading water in openrock boreholes is likely to preclude satisfactory measurements with an electric tape, a one inch drop pipeshould be installed in the well to the top of the pump in which accurate measurements can be made.

Wetted tape methodThis is the most accurate method of measuring water levels. The wetted tape method utilizes a cali-

brated steel tape with a weight attached to the end of the tape. The lowest 2 to 3 feet of the tape is coatedwith carpenter’s chalk. Water level measurements are obtained by noting the length of tape dropped intothe water and subtracting this from the reading of the tape held at the measuring point (usually the top ofcasing). Disadvantages of this method include:1) Water depths below 100 feet are difficult to measure because the amount of tape to be withdrawn each

time becomes cumbersome.2) Because initial water level readings are typically one minute apart, frequency of dropping and removing

the tape is also cumbersome.3) Cascading water in wells can distort accuracy of reading on chalked portion of the tape.

Airline methodThe airline method involves installation of a small diameter tube (airline) in the well which is pressur-

ized by a small air compressor or tire pump. By knowing the length of the tube and reading the pressuregauge at various times during the pump test, relatively accurate readings of water level in the well can becalculated. Pressure gauges calibrated in feet of water are available and are recommended for best results.

The dependability of measurement varies with the accuracy of the pressure gauge and the care at whichthe airline is installed in the well. The airline must be vertical without kinks or coils and must be airtight toensure as accurate readings as possible. The airline should be purged each time a measurement is taken toensure accuracy.

The operation of an airline is shown on Figure 1. The airline itself is a small diameter metal or plastictube installed below the maximum pumping level (usually down to or near the pump intake), fitted at thesurface with a Schrader (tire) valve and pressure gage. In operation, air (or an inert gas) is pumped into theairline until a maximum pressure is reached on the gage, at which point the air will be bubbling out thebottom of the airline. The pressure at the gage is then equal to the distance from the water level in the wellto the bottom of the airline and, by knowing the length of the airline, this distance can be subtracted from

59

that length to obtain the depth to waterbelow the gage. If the gage reads in psi itmust first be converted to feet by multi-plying by 2.31. During falling water levelconditions (drawdown) it is usually notnecessary to keep adding air for eachmeasurement because the expanding aircontinues to evacuate the line; duringrising water levels (recovery) it is neces-sary to re-pressure the line for eachobservation. The source of air must havesufficient pressure to blow all the waterout of the airline. A typical manual tirepump cannot usually develop morepressure than about 40 psi (or about 90feet); for airlines submerged to greaterdepths it may be necessary to use a motor-driven compressor, or a tank or cylinder ofcompressed air or nitrogen, to obtain atrue reading.

Flow Rate Measurement

Circular orifice weirA circular orifice weir is the device

used most often to measure the dischargefrom a pumping test. The advantage ofthis method is its simplicity and the abilityto quickly and accurately determinepumping rates and make adjustments tohold a constant rate.

Figure 2 is an illustration of thedimensional requirements to construct anorifice weir. The orifice is a round holewith clean, square edges in the center of acircular steel plate. The plate should be 1/

16 inch thick around the circumference of the hole and should be fastened against the outer end of thedischarge pipe so that the orifice is centered on the pipe. The end of the pipe must be squarely cut so thatthe plate is vertical. The bore of the pipe must be smooth and free of obstructions that would cause turbu-lence. The discharge pipe must be straight and level for a distance of 6 feet from the orifice. The pipe wallshould be tapped midway between the top and bottom with a 1/4 inch hole exactly 24 inches from theorifice plate. Any burrs inside the pipe from drilling and tapping the hole should be filed off.

A manometer tube should be fitted to the hole with a 1/4 inch nipple in order to measure the head ofwater in the discharge pipe. The manometer tube should be clear plastic tubing about 5 feet long. Thenipple, which is screwed into the hole, must not protrude inside the discharge pipe. A scale divided ininches should be fastened to the pipe or securely fastened to a stake driven into the ground so that the headfrom the center of the discharge pipe can be measured directly. The water level in the manometer tubeindicates the pressure head caused by the orifice plate when water is pumped through the discharge pipe.

For any given size of orifice/discharge pipe, the rate of flow at various pressure heads can be deter-mined from standard tables available in numerous references. This method of measurement of flow rates isrecommended for most circumstances.

Commercial water metersA commercial water meter is a reliable means of measuring large discharge rates. Its primary disadvan-

tage results from the delay in obtaining values at the start of the test when the pumping rate is beingadjusted to the desired level. Another disadvantage is that it is a precision instrument which must be caredfor, and could become inaccurate if mishandled or abused. Meters used routinely should be calibrated or

D = Depth to water infeet belowpressure gage

P = Gage pressure(max.) in ft. ofwater

L = Length of airlinein ft.

D = L - P

(If gage reads in PSI,multiply PSI by 2.31 toget ft. of water)

Air

Waterlevel

Airline

D

P

L

01

2 3 45

Figure 1. Example of airline setup and operation.

60

checked regularly. The advantage of this method is the ability to record the total pumpage during a testperiod, particularly if maintaining a constant rate is difficult due to test conditions.

Container/timed methodThe container/timed method involves the use of a container of known volume and a timing device. To

determine the pump discharge rate, one observes the time it takes to fill a container of known volume. Thevolume divided by the time gives the discharge rate. While the container/timed method is a practicalmeans to determine discharge rate, it is generally useful only for low pumping rates. The disadvantage ofthis method is that instantaneous readings cannot be obtained and it is difficult and time consuming to usethis method to change or adjust pumping rates.

Weirs and flumesThis method can be used to measure flow from a well by constructing a constriction in a discharge

channel originating at the wellhead. The specifications and methods for use of weirs and flumes areavailable in numerous references. The accuracy of these discharge rate measurement devices can varyfrom plus or minus 10% or better. Great care must be taken in the construction and installation of thesedevices to ensure the best possible accuracy.

Simple Tests To Estimate Well Yield

Bailing test methodA bailer of known volume that is only slightly smaller than the well casing should be used. The static

level of the water in the well should be measured accurately. The well should then be bailed until the waterlevel can no longer be lowered and the bailing line should be marked with paint at a point level with thetop of the casing when the bottom of the bailer is just touching the water, (a fast falling bailer makes anaudible sound when it hits the water surface). A second mark should be made one bailer length above thefirst. Rhythmically bailing, the driller should lower the line precisely to the second mark on the cable eachtime, noting the elapsed time per round trip. The bailer should be full each time as it emerges from thewell. If the bailer is not full, it should not be lowered deeper; rather, the rate of bailing should be sloweduntil the bailer comes out full each time. The bailing rate in gallons per minute (gpm), equals the volumeof the bailer divided by the time per round trip. The bailing rate and the drawdown (water level repre-

61605958575616151413121110987654321

Orifice plate andpipe end-cap

1/8 – 3/8 in.

1/16 in.

Gate valve Piezometer tube

Detail of orifice plate

4 ft. minimum 24 in.

Scale

Figure 2. Detail of orifice weir construction.

61

sented by first mark on the bailing line minus the static level) should be recorded on the well log.When there is less depth of water in the well then the length of the bailer, it is impossible to follow the

above procedure. Instead, the amount of water in the bailer should be measured and related to a timedinterval of one minute for each time the bailer leaves the bottom of the well. An alternative method for awell that can be bailed dry is to measure the rate of recovery after the well is bailed down. By calculatingthe volume of water in the casing or borehole after 10 or 15 minutes of recovery and dividing by the timeof recovery, the maximum rate that the well will produce can be estimated.

Air blow test methodUsing this method the well should be tested for 30 minutes by introducing air in sufficient quantity to

blow the water out of the well. The discharge of the air should be at the bottom of the hole through thedrill stem. A deflector should be placed at the top of the well casing to deflect the water downward outsidethe well. A dike should be constructed around the well to contain the deflected water, and a discharge pipeshould be placed near the top of the dike and the water allowed to discharge through it. A container ofknown volume should be used to collect the water from the discharge for a measured period of time andthe rate (gpm) should be calculated from this information and recorded on the well log.

A disadvantage of this method is that it is impossible to get an accurate drawdown measurement.However, the water level should be measured as quickly as possible after shutting off the air flow to allowfor estimation of the amount of drawdown that was associated with the flow rate. An alternative methodfor low yielding wells is to blow the well for 30 minutes and measure the recovery for 10 or 15 minutes.The maximum rate that the well can produce can be estimated by dividing the recovery time into thevolume of water that has filled the casing or borehole.

Air lift test methodUsing this method, air should be introduced through an airline with upward pointing jets inside of an

eductor pipe placed at the bottom of the well. The submergence (length of the eductor pipe from the lowerend to the pumping level as related to the total length of the eductor pipe) should be at least 60 percent.Drawdown in the well in which the airlift pump is working can be measured between the eductor pipe andthe well casing by any of the conventional methods. A deflector should be placed at the top of the well todeflect the water downward outside of the well. A dike should be constructed around the well and the flowrate should be measured as described for the air-blow test method. The advantage of airlift over the air-blow test method is the ability to accurately measure drawdown.

Variable pumping rate methodA test pump that can produce more than the desired pumping rate should be set at the depth of the

lowest producing zone in the well and the well should be pumped until the pump breaks suction. The ratethen should be slowly decreased until the pumping level stabilizes approximately 2 feet above the pumpintake for a period of at least 5 minutes. The pumping rate then should be decreased by 5 percent and thewell should be pumped at this rate until the pumping level stabilizes for 1 hour. The discharge rate anddrawdown thus established should be maintained for at least 4 hours. This pumping rate can be consideredthe available production rate of the well, and the observed pumping level during the test can be consid-ered the production pumping level for the well.

Pumping Test To Evaluate Well Performance

Step-drawdown testsThe step-drawdown test typically is used to examine the performance of wells by theoretically separat-

ing drawdown into components produced by laminar (aquifer loss) and turbulent (well loss) flow. Steptests are the single most useful pumping test tool for benchmarking and then assessing well performancechanges over time. It is important that subsequent tests be run at comparable discharge rates to makecomparisons on values such as specific capacity. If personnel are running a test that will be evaluated bya hydrogeologist not a the test and supervising, it is necessary to provide all drawdown data and not justfinal drawdown points in a step (Driscoll, 1986 and NGWA, 1998). The well should be pumped at severalsuccessively higher pumping rates and the drawdown for each rate, or step, is recorded. The incrementalrate increases should be approximately the same and the time duration for each step should be one hour,but this might vary from 30 minutes to 2 hours for a particular well depending upon how fast pumpinglevels stabilize after each rate increase. The number of steps may be from as few as 3 to as many as 8.

62

Step tests are sometimes used to determine or verify the depth of significant water producing zones inrock boreholes. The same stepwise incremental increase of equal rate and pumping time is used until thepump breaks suction or the maximum pump capacity is reached. Disproportionate increases in drawdownindicate water producing zones and once the pumping level is lowered below a major producing zone, thedrawdowns accelerate significantly. Upon shutdown of the pump, depth to water zones can be accuratelyidentified by listening to cascading water in the borehole and noting the water level when the soundchanges or stops during recovery.

Constant rate tests

PreparationA test pump should be selected that is capable of producing at least 1.5 times the desired or anticipated

well capacity at the maximum pumping level in the well. Provisions should be made at the wellhead tofacilitate easy access for measuring water levels. A control valve should be installed at the wellhead in thedischarge line before the flow measuring device to provide for making adjustments to the pumping rates.Provisions should be made to ensure uninterrupted pumping during the test. If direct current is used, theappropriate switches or automatic controls within the circuit should be locked out to preclude an inadvert-ent shutdown of power. If an electric generator or direct drive power unit is used to operate the test pump,provisions must be made to ensure timely refueling and continued operation of the system for the durationof the test. Discharge piping should be provided to convey the water to a natural point of drainage awayfrom the well. Depending upon the hydrogeologic setting, special provisions may be required to ensurethat discharge water is not recirculated and give a false response to water level changes due to pumping.Ideally, the flow measuring device should be near the control valve and wellhead. If a long discharge lineis required, it should be free of leaks, and if the flow measuring device must be placed at the end of thedischarge line, special provisions may be required to ensure timely and accurate adjustments to the flowrate.

Test RateA pumping rate should be selected that will stress the well during the pumping test more than it will be

stressed during normal operation. Typically, the test rate should be about 1.5 times the planned or desiredwell capacity. For sand and gravel wells this is consistent with well development objectives, i.e. pumpingthe well at least 50 percent above design rate to remove fines from the screened area to ensure completedevelopment. For rock wells, the test rate should be selected that will maintain pumping levels above themajor water producing zone(s) during the test. Step test data can be used to determine the most appropriaterate for a constant rate test. If step test data is not available, a pump trial should be performed to establisha feasible pumping rate for the constant rate test to preclude a rate change due to failure to select theproper test rate. It is essential that the pumping rate be held constant so that water level changes can beanalyzed correctly.

Test DurationTypically a pumping test of a minimum 24 hours in duration is required (depending on the aquifer, a

much longer test may be needed, e.g. unconfined alluvial systems) to conclusively evaluate the perfor-mance characteristics of a well and enable reliable predictions of long term time-drawdown relationshipsand sustainable well yield. However, for some low use requirements or for well performance evaluations,properly run and analyzed shorter tests (6, 8, or 12 hours) may be sufficient. The determination of anappropriate length of time for a pumping test under these circumstances should be based on the requiredpumping rates and operating time necessary to meet the anticipated daily demand.

Recovery DataWhenever practical, recovery data should be collected to verify the accuracy of pumping data. Often,

the recovery data will be more consistent and reliable if it has not been possible to maintain a constant rateduring the test. Recovery measurement should be measured at the same frequency and for the sameduration as the pumping period. If the drawdown data collected during the test is considered reliable,recovery data is less important and not essential.

Pumping Tests To Evaluate Aquifer CharacteristicsPumping tests to evaluate aquifer characteristics require more elaborate preparation, data collection,

and analysis. Typically, the test duration for confined (artesian) conditions will be 24 hours in duration and

63

tests of aquifer systems under unconfined (water table) conditions will be 72 hours in duration. These testsusually involve the installation of several observation wells in various configurations (depth and spacing)with respect to the pumping well. Collection of background data is usually very important in order toevaluate natural trends and fluctuations of ground water levels before, during, and after the pumping test.Additional data to be collected may include barometric pressure changes, river levels, precipitation, andany changes in pumpage that may affect ground water levels in the pumping well and observation wells.

Data Collection And Record KeepingBefore starting a pumping test, the complete program for depth-to-water measurements should be laid

out. When using multiple observation wells it is not necessary to make measurements in all wells simulta-neously, but watches used for timing the measurements should be synchronized so that the time of eachreading can be referenced to a common start time. The date, clock time, elapsed pumping time, and depthto water should be recorded for each measurement. Any readings and calculations made to determinedepth to water such as used for the wetted tape method or corrections for tape length should be recorded topreclude errors in field calculations. Water level measurements should be made to the nearest 0.01 foot.Field forms should be provided with columns for each type of data recorded. Other data such as pumpingrates, the size of the orifice weir, manometer hose readings, air line length, height and description ofmeasuring points, and personnel collecting the data should be recorded on the forms. Preprinted pumpingtest forms for pumping tests longer than 8 hours in duration are available from the Ohio Department ofNatural Resources, Division of Water. The measurement intervals are similar to those shown below(especially for the first 60 minutes). These forms can be obtained free of charge by contacting the Divi-sion of Water’s Water Resources Section at 614-265-6739.

Early test data is extremely important and as much information as possible should be obtained in thefirst 10 minutes of pumping. The following time intervals are recommended for water level measurements:

Time After Pumping Started or Stopped (in minutes) Time Interval Between Measurements (in minutes)0-10 0.5-1

10-15 115-60 560-120 10120-180 20180-300 30

300-1440 301440-termination of test 240 (4 hrs.)

64

Table 1. Estimating Water Usage

Place GPD per Unit Occupancy Type

Apartments ........................................................................ 250 .................... one bedroomApartments ........................................................................ 300 .................... two bedroomApartments ........................................................................ 350 .................... three bedroomAssembly Halls ................................................................. 2 ........................ per seatBowling Alleys (no food service) ....................................... 75 ...................... per laneChurches (small) ............................................................... 4 ........................ per sanctuary seatChurches (large w/kitchen) ............................................... 6 ........................ per sanctuary seatCountry Clubs ................................................................... 50 ...................... per memberDance Halls ....................................................................... 2 ........................ per personDrive-In Theaters .............................................................. 5 ........................ per car spaceFactories (no showers) ..................................................... 25 ...................... per employeeFactories (w/showers) ....................................................... 35 ...................... per employee

Food Service Operations Ordinary restaurant (no 24 hr) ...................................... 35 ...................... per seat

24-hr. restaurant .......................................................... 50 ...................... per seatBanquet rooms ............................................................ 5 ........................ per seatRestaurant along freeway ............................................ 100 .................... per seatTavern (very little food service) .................................... 35 ...................... per seatCurb service (drive-in) ................................................. 50 ...................... per car spaceVending machine restaurants ...................................... 100 .................... per seat

Homes in Subdivisions ..................................................... 400 .................... per dwellingHospitals (no resident personnel) ..................................... 300 .................... per bedInstitutions (residents) ....................................................... 100 .................... per personLaundries (coin operated) ................................................. 400 .................... per std. size machineMobile Home Parks .......................................................... 300 .................... per mobile home spaceMotels ............................................................................... 100 .................... per unitNursing & Rest Homes ..................................................... 150 .................... per patientNursing & Rest Homes ..................................................... 100 .................... per resident employeeNursing & Rest Homes ..................................................... 50 ...................... per nonresident emp.Office Buildings ................................................................. 20 ...................... per employeeRecreational Vehicle Parks & Camps ............................... 125 .................... per trailer or tent spaceRetail Store ....................................................................... 20 ...................... per employeeSchools-Elementary .......................................................... 15 ...................... per pupilSchools-High & Junior High .............................................. 20 ...................... per pupilService Stations ................................................................ 1000 .................. first bay or pump islandService Stations ................................................................ 500 .................... additional bay or pump islandShopping Centers (no food service or laundries) ............. 0.2 ..................... per sq. ft. of floor spaceSwimming Pools (average) ............................................... 4 ........................ per swimmerWith hot water showers .................................................... 6 ........................ per swimmerTravel Trailer Parks & Camps ........................................... 125 .................... per trailer or tent spaceVacation Cottages ............................................................. 50 ...................... per personYouth & Recreation Camps .............................................. 50 ...................... per person

65

Appendix IVWater Sample Collection

Coliform bacteria samplingWater samples for bacteriological analysis should be collected in a sterile sample bottle provided by the

laboratory that will perform the analysis. The sample bottle should not be rinsed prior to collection of thesample. Great care should be taken to prevent contamination of the sample that may produce erroneousresults. The following is the recommended total coliform sampling procedure:(1) Select a tap such as a small valve to collect samples. Do not sample from hoses. Avoid taps that leak

at the stem.(2) Sanitize the nozzle of the tap with a chlorine solution.

(a) Use a 5.25% sodium hypochlorite solution such as CloroxTM liquid bleach. Do not use chlorinesolutions with special scents. To prepare a sanitizing solution that will contain about 400 mg/L ofavailable chlorine from the 5.25% sodium hypochlorite, add one ounce of bleach to one gallon ofwater (or 1 tablespoon per half gallon). Store the mixed solution in a tightly closed screw cappedcontainer. The solution should be discarded and remade six months after preparation. Strongersolutions can be used; however, some tap discoloration may result.

(b) Open the sample tap long enough to flush water in the drop pipe. Close the valve.(c) Apply the sanitizing solution to the nozzle. This can be accomplished by either using a spray

bottle or a plastic bag.i. Using a spray bottle, saturate the tap opening with sanitizing solution then wait at least two

minutes before proceeding, orii. Place a bag over the nozzle and hold the top of the bag tightly on the tap. Alternately squeeze

and release the bag to flush the solution in and out of the tap. Do this for two minutes. Afresh solution and bag must be used to sanitize each tap.

(d) Flush the tap. The sample to be collected is intended to be representative the water in the well.The tap must be fully open and the water run to waste for enough time (1-2 well bore volumes) toallow for adequate flushing of the drop pipe.

(e) Reduce the flow from the tap. This will allow the sample bottle to be filled without splashing.(f) Remove the cap from the sample bottle.

i. Grasp the bottom of the sample bottle.ii. Remove the cap and hold the exterior of the cap between your fingers while filling the

sample bottle. Take care not to touch the mouth of the bottle or the inside of the cap withfingers or the sample could become contaminated.

iii. The bottle must be open only during the collection of the sample.(g) Fill the sample bottle.

i. Do not rinse out the bottle before collecting the sample. Do not remove any pills from thebottle. The bottle contains a small amount of sodium thiosulfate to neutralize any chlorinethat may be in the water.

ii. Do not touch the rim or mouth of the bottle during collection of the sample.iii. Do not overflow the bottle. Fill the bottle to within 1 inch of the top.

(h) Immediately recap the sample bottle tightly.(i) If there is any question as to whether a sample or bottle has become contaminated during collec-

tion of the sample, the bottle should be discarded and a new sample collected in a new samplebottle.

(j) All samples should be kept cool but not frozen. Deliver the sample to the laboratory as soon aspossible. The laboratory must receive the sample within 30 hours after collection so analysis can beinitiated. Samples greater than 30 hours old are considered invalid samples. Allow the laboratoryadequate time to analyze the sample.

A bacterial sample report form is supplied with each sample bottle. The top half of the bacterial samplereport should be filled out by the individual collecting the sample. Each completed bacterial sample report

66

should be attached to the respective finished sample by wrapping the report around the sample bottle witha rubber band.

As noted above, all microbiological analysis conducted on a public water system water source must beanalyzed by a laboratory certified for such analysis by the Ohio EPA. Contact the appropriate districtoffice of the Ohio EPA, Division of Drinking and Ground Waters for a current list of approved laborato-ries.

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Appendix VWell Disinfection

Disinfection of a Drilled Well1. Determine the amount of water in the well by multiplying the gallons per foot by the total depth of water in the well

in feet. This information can be obtained by measuring the depth to the water level in the well, and subtracting thisnumber from the total well depth (Example: Total well depth is 100 feet, depth to water from the ground surface is 40feet, therefore 100-40 = 60 feet of water in the well). This is the total depth of water in the well. Table 1 provides thegallons of water per foot in a well based on the well diameter. For example, a well with a six inch diameter contains1.5 gallons of water per foot. If there is 60 feet of water in the well, multiply 1.5 by 60 (1.5 X 60 = 90). If the totalwater depth cannot be obtained, assume a water depth of 100 feet.

2. For each 100 gallons of water in the well, use the amount of chlorine (unscented liquid or granules) indicated in Table2. Mix the total amount of liquid or granules with about 10 gallons of water.

3. Pour the solution into the top of the well before the seal is installed.4. Connect a hose from a faucet on the discharge side of the pressure tank to the well casing top. Start the pump. Spray

the water back into the well and wash the sides of the casing for at least 15 minutes.5. Systematically open every faucet and fixture in the system and let the water run until the smell of chlorine can be

detected. Include both hot and cold water valves. Then close all the faucets and seal the top of the well.6. Let stand for a minimum of 6-8 hours, preferably overnight.7. After letting the water stand for the contact period, open the hose spigot and discharge water to the ground

surface or a drainage ditch until the chlorine odor disappears. Turn on all remaining faucets and fixturesand let the water run until all odor of chlorine disappears. Adjust the flow of water from faucets or fixturesthat discharge into septic tank systems to a low flow to avoid overloading the disposal system.

Calculation and ExamplesTo determine the amount of liquid chlorine bleach needed to achieve a desired concentration, the following

equation may be used:

Table 2. Amount of Chlorine Added to 100 Gallons of Water for Disinfection

Chlorine concentration(parts per million or mg/l)

Gallons of 5.25% sodiumhypochlorite liquid bleach

Pounds of dry calciumhypochlorite

Minimumcontact time

500mg/l 1 gallons 0.75 pounds 8 hours

250mg/l 0.5 gallons 0.38 pounds 8 hours

Diameter of Well (inches) Gallons per Foot of Water

3 0.374 0.655 1.06 1.58 2.6

10 4.1

Table 1. Volume of Water in Well

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Example: Desired concentration of 5.25% liquid bleach to disinfect a one hundred foot deep well withfive inch casing and a static water level at sixty feet.

Therefore V= .38 gallons of 5.25% liquid bleach needed to get a concentration of 500 mg/l in a 40gallon column of water.

There are other methods that can be used to disinfect wells. Solid calcium hypochlorite tablets can be placeddirectly in the well so that the solid chlorine will sink to the bottom of the well and dissolve there. Chlorinetablets can also be placed in a mesh bag or perforated pipe and run up and down the water column until it iscompletely dissolved. Calcium hypochlorite used to disinfect wells will have a concentration of either 60, 65, or70 per cent available chlorine. Below is an equation similar to the one used for liquid bleach can be used todetermine the proper amounts of calcium hypochlorite to use in a well for shock disinfection.

Disinfection of a Dug or Bored Well1. Use Table 3 to calculate how much bleach (liquid or granules) to use.2. To determine the exact amount to use, multiply the amount of disinfectant needed (according to the diameter of

the well) by the total depth of water in the well. The total depth of water in the well can be calculated bysubtracting the depth to the water measured from the ground surface from the total depth of the well. Forexample, a well 5 feet in diameter requires 6 cups of bleach per foot of water. If there is 30 feet of water in thewell then multiply 6 by 30 to determine the total cups of bleach required (6 X 30 = 180 cups). There are sixteencups in each gallon of liquid bleach (For the previous example this equals 180 cups/16 cups per gallon = 11.25gallons).

3. Add this total amount of disinfectant to about 10 gallons of water. Splash the mixture around the wall or lining ofthe well. Be certain the disinfectant solution contacts all parts of the well.

4. Seal the top of the well.5. Open all faucets and pump water until a strong odor of bleach is noticeable at each faucet. Then stop the pump

and allow the solution to remain in the well overnight.

water volume(gallons in well)

8.33 lbs(weight of 1gal. water)

desired disinfectant concentration(mg/l in decimal)

Volume(gallons of

disinfectant) 8.33 lbs

X X=

Disinfectant concentration(% in decimal)

Sodium Hypochlorite (liquid bleach)

40 8.330.005

.388.33 lbs

X X= 0.0525

Diameter of Well (feet)Amount of 5.25% laundrybleach per foot of water

Amount of 70% chlorine gran-ules per foot of water

3 0.15 gallons (2.5 cups) 2 ounces

4 0.25 gallons (4 cups) 3 ounces




8 1 gallons 10 ounces

10 1.5 gallons 1 pound

Table 3. Quantity of Bleach for a Bored or Dug Well (1000 ppm)

water volume(gallons in well)

8.33 lbs(weight of 1gal. water)

desired disinfectant concentration(mg/l in decimal)Weight in pounds of

Calcium Hypochlorite X X=Disinfectant concentration

(% in decimal)

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6. The next day, connect a hose to an outside spigot and discharge water until the odor of chlorine disappears. Thenturn on all faucets, continuing to discharge water until the chlorine odor disappears. Adjust the flow of waterfaucets or fixtures that discharge to septic systems to a low flow to avoid overloading the disposal system.

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Appendix VIMonitoring Well Design and Installation1

In order to collect representative ground water samples, it is necessary to construct monitoring wells togain access to the subsurface. This chapter covers installation and construction of single-riser/limitedinterval wells, which are designed such that only one discrete zone is monitored in a given borehole. It isimportant that efforts focus on intervals less than 10 feet thick and be specific to a single saturated zone.

All monitoring wells should be designed and installed in conformance with site hydrogeology,geochemistry, and contaminant(s). While it is not possible to provide specifications for every situation, itis possible to identify certain design components. Figure 1 is a schematic drawing of a single-riser/limitedinterval well. The casing provides access to the subsurface. The intake consists of a filter pack and screen.The screen allows water to enter the well and, at the same time, minimizes the entrance of filter packmaterials. The filter pack is an envelope of uniform, clean, well-rounded sand or gravel that is placedbetween the formation and the screen. It helps to prevent sediment from entering the well. Installation of afilter pack and screen may not be necessary for wells completed in competent bedrock. The annular seal isemplaced between the borehole wall and the casing and is necessary to prevent vertical movement ofground water and infiltration of surface water and contaminants. Surface protection, which includes asurface seal and protective casing, provides an additional safeguard against surface water infiltration andprotects the well casing from physical damage.

Design of Multiple-Interval SystemsIt is often necessary to sample from multiple

discrete intervals at a given location if more thanone potential pathway exists or a saturated zone isgreater than 10 feet thick. Multiple-intervalmonitoring can be accomplished by installingsingle-riser/limited interval wells in side-by-sideboreholes (well clusters) or using systems thatallow sampling of more than one interval from thesame borehole (multilevel wells, well nests, orsingle-riser/flow-through wells).

Well ClustersWhen monitoring multiple intervals at one

location, single-riser/limited interval wells shouldbe installed in adjacent, separate boreholes. Thesewell clusters can be used to determine verticalgradients when distinct differences in head exist.They may be used to monitor discrete zones orevaluate chemical stratification within a thickzone. If flow direction has been determined priorto installation, the shallow well should be placedhydraulically upgradient of the deeper well toavoid the potential influence on its samplescaused by the presence of grout in the annularspace of the deeper well.

Multi-Level WellsMultilevel wells allow sampling of more than

one interval in a single borehole. Individual tubesrun from sampling levels to the surface. Theselevels are isolated within the well either bypackers or grout. Probes, lowered into the casing,can locate, isolate and open a valve into a portcoupling to measure the fluid pressure outside thecoupling or obtain a sample.1 Modified from Chapter 7 of the Ohio Environmental Agency’s “Technical Manual for Hydrogeologic Investigations and

Ground Water Monitoring”, 1995.

Figure 1. Cross-section of a typical single-riser/limited interval monitoring well.

Protectiveseal

Maximum frost line

Annular SealNeat cement/bentonite

or bentonite

Optional secondaryfilter pack

(very fine sand)

Primary filter pack

Filter pack seal(bentonite)

Weep hole

Inner cap

Bumper guards

Outerlocking cap

Surface seal

Well casing

Well screenBottom cap

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The use of multiple-level monitoring wells in Ohio has been limited due to: 1) cost of installation, 2)difficulty in repairing clogs, and 3) difficulty in preventing and/or evaluating sealant and packer leakage.Detailed work plans (including construction and installation, methods to measure water levels and obtainsamples, references to situations where these types of wells have been used successfully, and advantagesand disadvantages) should be submitted prior to installing multilevel systems. Until more site-specific datais available concerning their performance, multilevel wells should only be considered when a single zonehaving no to little vertical flow is being monitored at different depths.

Nested WellsNested wells involve the completion of a series of single-riser wells in a borehole. Each well is screened

to monitor a specific zone, with filter packs and seals employed to isolate the zones. Nested wells are notrecommended because they are difficult to install in a manner that ensures that all screens, filter packs, andseals are properly placed and functioning. It is more efficient to install single-riser wells for each interval toensure that representative samples can be collected. Aller et al. (1991) indicated that individual completionsgenerally are more economical at depths less than 80 feet. According to Dalton et al. (1991), the cost ofinstalling well clusters is usually only marginally higher than the cost for nested wells. Well clusters canenable savings on sampling and future legal costs that may be necessary to prove the accuracy of nestedwells.

Single Riser/Flow-Through WellsSingle riser/flow-through wells are monitoring wells that, in general, are screened across the entire

thickness of a water-bearing zone. These wells are typically small in diameter and provide a “transparent”cross-section of the flow field (Aller et al., 1991). If purging is performed immediately before sampling,only composite water samples are yielded, which are not adequate for most monitoring studies. If natural,flow-through conditions can be maintained, and if a sampling device can be lowered with minimal distur-bance of the water column, vertical water quality profiles potentially can be identified. To achieve anddocument the collection of such samples is very difficult, however, and the resulting data may be ques-tioned. Furthermore, these wells are conducive to allowing cross-contamination between different zonesand, therefore, should not be used in contaminated areas. Flow-through wells are not recommended.

CasingThe purpose of casing is to provide access to the subsurface for sampling of ground water and measure-

ment of water levels. A variety of casing has been developed. Items that must be considered during welldesign include casing type, coupling mechanism, diameter, and installation.

Casing TypesThere are three categories of casing commonly used for ground water monitoring, including

fluoropolymers, metallics, and thermoplastics (Aller et al., 1991). All have distinctive characteris-tics that determine their appropriateness.

FluoropolymersFluoropolymers are synthetic “plastics” composed of organic material. They are resistant to chemical

and biological attack, oxidation, weathering, and ultraviolet (UV) radiation. They have a broad usefultemperature range, a high dielectric constant, a low coefficient of friction, display anti-stick properties,and have a greater coefficient of thermal expansion than most other plastics and materials (Aller et al.,1991). A variety of fluoropolymers are marketed under various trademarks. Some manufacturers use onetrade name to refer to several of their own materials, which may not always be interchangeable in serviceor performance (U.S. EPA, 1992). Standard properties of the various materials have been provided byNielsen and Schalla (1991) and Aller et al. (1991).

The most common fluoropolymer used for monitoring wells is polytetrafluoroethylene (PTFE).It can withstand strong acids and organic solvents and, therefore, it is useful for environmentscharacterized by the presence of these chemicals. It maintains a low tensile strength, which theo-retically limits installation of Schedule 40 PTFE to an approximate depth of 2502. It is also veryflexible, which makes it difficult to install with the retention of straightness that is needed to ensuresuccessful insertion of sampling or measurement devices. Dablow et al. (1988) found that theductile nature of PTFE can result in the partial closing of screen slots due to the compressive forcesof the casing weight. This makes slot size selection very difficult. The inert nature of PTFE often

2 The maximum depth for PTFE casing is dependent on site hydrogeology. If the casing largely penetrates unsaturated soils, thedepth may be limited to approximately 100 feet. However, if the casing is placed mostly in water-bearing zones, then depthmay be as great as 375 feet.

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prevents the annular seal from bonding with the casing completely, which can allow infiltration ofsurface water. PTFE is costly, generally ten times more expensive than thermoplastics.

MetallicsMetallic materials include low carbon, carbon, galvanized, and stainless steel. Metallics are

very strong and rigid and can be used to virtually unlimited depths. Corrosion problems are themajor disadvantage for low carbon, carbon, and galvanized casings. Electrochemical and chemicalattack alters water sample quality. U.S.EPA (1992) has listed the following as indicators ofcorrosive conditions (modified from Driscoll, 1986):

• Low pH (< 7.0).• Dissolved oxygen exceeds 2 ppm.• Hydrogen sulfide in quantities as low as 1 ppm.• Total dissolved solids (TDS) greater than 1000 ppm.• Carbon dioxide exceeds 50 ppm.• Chloride (Cl-), bromide (Br-), and fluoride (F-) content together exceeds 500 ppm.According to Barcelona et al. (1983), flushing before sampling does not minimize the bias of

low carbon steel due to the inability to predict the effects of disturbed surface coatings andcorrosion products accumulated at the bottom of the well. Due to their high corrosion potential, allmetallics except stainless steel are unacceptable for monitoring wells.

Stainless steel is manufactured in two common types, 304 and 316. Type 304 is composed ofiron with chromium and nickel. Type 316’s composition is the same as Type 304’s, but includesmolybdenum, which provides further resistance to sulfuric acid solutions. Stainless steel is readilyavailable in a wide variety of diameters.

Stainless steel can perform quite well in most corrosive environments. In fact, oxygen contactdevelops an external layer that enhances corrosion resistance (Driscoll, 1986). Yet, under verycorrosive conditions, even stainless steel can corrode and release nickel and chromium intoground water samples (Barcelona et al., 1983). Combinations and/or extremes of the factorsindicating corrosive conditions generally are an indication of highly corrosive environments. Forexample, Parker et al. (1990) found that both 304 and 316 showed rapid rusting (<24 hrs.) whenexposed to water containing chloride above 1000 mg/l. Like PTFE, stainless steel is relativelyexpensive in comparison with thermoplastics Nielsen and Schalla (1991) and Aller et al. (1991)provided additional information on the properties of stainless steel.

ThermoplasticsThermoplastics are composed of large, synthetic organic molecules. The most common type

used for monitoring wells is polyvinyl chloride (PVC), while a material used less often is acry-lonitrile butadiene styrene (ABS). These materials are weaker, less rigid, and more temperature-sensitive than metallics. Thermoplastics are very popular due to their light weight, high strength toweight ratio, low maintenance, ease of joining, and low cost.

Common, acceptable PVC types are Schedule 40 and Schedule 80. The greater wall thicknessof Schedule 80 piping enhances durability and strength, provides greater resistance to heat attackfrom cement, and allows construction of deeper wells. Only rigid PVC should be used for moni-toring wells. Flexible PVC is composed of a high percentage of plasticizers (30 - 50%), whichtend to degrade and contaminate samples (Jones and Miller, 1988). All PVC casing should meetStandard 14 of NSF International. This standard sets control levels for the amount of chemicaladditives to minimize leaching of contaminants (NSF International, 1988). Additional specifica-tions have been provided by Nielsen and Schalla (1991) and Aller et al. (1991).

Drawbacks of PVC include brittleness caused by ultraviolet (UV) radiation, low tensilestrength, relative buoyancy in water, and susceptibility to chemical attack. It is immune tocorrosion and is resistant to most acids, oxidizing agents, salts, alkalies, oils, and fuels(NWWA/PPI, 1981). Additionally, Schmidt (1987) showed that no degradation of PVCoccurred after six months immersion in common gasolines. However, studies have shown thathigh concentrations (parts-per-thousand or percentage concentrations) of tetrahydrafuran,methyl ethyl ketone, methyl isobutyl ketone, and cyclohexane degrade PVC (Nielsen andSchalla, 1991). Barcelona et al. (1983) reported that low molecular weight ketones, alde-hydes, amines, and chlorinated alkenes and alkanes may cause degradation. There is a lack ofpublished information regarding the concentrations of these compounds at which deteriora-

73

tion is significant enough to affect either the structural integrity of casing or ground watersample quality.

Type SelectionMany regulated parties choose PVC casing because of its lower cost; however, well integrity and

sample representativeness are more important criteria. The high cost of analysis and the extreme precisionof laboratory instruments necessitate the installation of wells that produce representative samples. Aboveall, the burden of proof is on the regulated party to demonstrate that casing is appropriate. The properselection can be made by considering casing characteristics in conjunction with site conditions.

Casing characteristics include strength, chemical resistance and chemical interference potential. The strengthmust withstand the extensive tensile, compressive, and collapsing forces involved in maintaining an openborehole. Since the forces exerted are, in large part, related to well depth, strength often is important whenplanned depth exceeds the maximum range of the weakest acceptable material (100 to 375 ft. - PTFE). In theseinstances, either stainless steel or PVC should be chosen. Strength can be the overriding factor because theconcern for chemical resistance and interference become insignificant if an open borehole cannot be maintained.Nielsen and Schalla (1991) provided specific strength data for commonly used materials.

The casing also must withstand electrochemical corrosion and chemical attack from natural groundwater and any contaminant(s). Chemical resistance is most important in highly corrosive environments,when contaminants are present at extremely high levels, and when wells are intended to be part of a long-term monitoring program. For extended monitoring in corrosive environments, PTFE and PVC are pre-ferred over stainless steel because of the potential for the metallic material to degrade. If high concentra-tion of organics (parts per thousand) are present, either PTFE or stainless steel should be selected. U.S.EPA (1992) recommended that PVC not be used if a PVC solvent/softening agent is present or the aqueousconcentration of a solvent/softening agent3 exceeds 0.25 times its solubility in water. It is suitable in mostsituations where low (parts per billion to low parts per million) levels of most organic constituents arepresent (Nielsen and Schalla, 1991).

The casing also should not interfere with sample quality by adding (leaching) or removing contami-nants. In most cases, the magnitude of this interference is a function of the ground water’s contact timewith the casing. The longer the contact, the greater the potential for leaching and sorption. Various studieshave been conducted [Barcelona and Helfrich (1988), Curran and Tomson (1983), Gillham andO’Hannesin (1989), Jones and Miller (1988), Miller (1982), Parker and Jenkins (1986), Parker et al.(1990), Reynolds and Gillham (1985), Schmidt (1987), Sykes et al. (1986), Tomson et al. (1979), Hewitt(1992, 1994), Parker and Ranney (1994)] to compare the sorbing and leaching characteristics of the threefavored materials. No conclusive results have been obtained to indicate that any one is best. Most of thesestudies involved contact lasting days, weeks, and even months and, therefore, the results cannot be corre-lated to field conditions where contact is often minimal because sampling is generally conducted soonafter purging.

In many cases, concern about sorption or leaching may be exaggerated. Barcelona et al. (1983) andReynolds and Gillham (1985) both concluded that the potential sorption biases for casing may be dis-counted due to the short contact after purging. Also, Parker et al. (1990) indicated that sorption of variousconstituents never exceeded 10 percent in the first 8 hours of their tests. They concluded that, on the basisof overall sorption potential for organic and inorganic compounds, PVC is the best compromise.

In summary, the appropriate casing should be determined on a case-by-case basis. PVC is acceptablewhen free product is not present and the solubility limits of organic contaminants are not approached (e.g.,levels that exceed 0.25 times the solubility). Ohio EPA recognizes the difficulty inherent in establishing a“cut-off” level for when aqueous concentrations of organics cause failure of PVC. To be certain thatcasing will retain integrity, particularly when monitoring is planned for long periods of time (e.g., 30years), Ohio EPA may require a more resistant casing when aqueous concentrations are relatively high butstill below the criteria mentioned above.

Hybrid WellsCasing not in contact with the saturated zone generally is not subject to attack. Therefore, it may be

possible to install less chemically resistant material above the highest seasonal water level and more inertmaterial where ground water continually contacts the casing. Such a “hybrid well” commonly is installedfor cost reduction reasons only. For example, when monitoring a zone with high concentrations of organiccompounds, stainless steel or PTFE could be installed opposite the saturated materials, while PVC could

3 Known PVC solvent/softening agents include: tetrahydrofuran, cyclohexane, methyl ethylketone, methyl isobutyl ketone,methylene chloride, trichloromethane, 1-1-dichloroethane, trichloroethene, benzene, acetone, and tetrachloroethene.

74

be used opposite the unsaturated materials. Thus, resistant, more expensive casing would be present wherecontact with highly contaminated ground water may occur, while less resistant, inexpensive casing wouldbe present where contact does not occur.

Different varieties of steel never should be installed in the same well. Each type is characterized by itsown electro-chemical properties. Installation of different types in contact can increase the potential forcorrosion.

Coupling MechanismsCasing sections should be connected using threaded joints that provide for uniform inner and outer

diameters along the entire length of the well. Such “flush” coupling is necessary to accommodate theinsertion of tools and sampling devices without obstruction and to help prevent bridging during theinstallation of the filter pack and annular seal. It should be noted that thread types vary between manufac-turers and matching can be difficult. A union among non-matching joints should never be forced, other-wise structural integrity of the joint and the entire well could be compromised. To alleviate these prob-lems, the American Society of Testing and Materials has developed Standard F 480-90 (1992) to create auniformly manufactured flush-threaded joint. Most manufacturers now produce the F 480 joint, which isavailable in both PVC and stainless steel.

It is recommended that either nitrile, ethylene propylene, or Viton O-rings be used between sections toprevent the seal and/or affected water from entering (Nielsen and Schalla, 1991). Nielsen and Schalla(1991) indicated that Teflon tape can be used in place of O-rings, although it does not ensure as good aseal. Solvent cements should never be used because they are known to leach organics. Although weldingstainless steel can produce a flush joint that is of equal or greater strength than the casing itself, thismethod is not recommended due to the extra assembly time, welding difficulty, corrosion enhancement,ignition danger, and the potential to lose materials into the well (Nielsen and Schalla, 1991).

Threaded steel casing provides inexpensive, convenient connections. It should be noted that threadedjoints reduce the tensile strength of the casing; however, this does not cause a problem for most shallowwells. Also, threaded joints may limit or hinder the use of various sampling devices when thin-walledstainless steel (Schedules 5 and 10) is employed. Thin-walled casing is too thin for threads to be ma-chined, so the factory welds a short, threaded section of Schedule 40 stainless steel pipe to the end of thethin-walled pipe. These joints are made to be flush on the outside, but not the inside.

If hybrid wells are installed, it is essential that the joint threads be matched properly. This can beaccomplished by purchasing casing screen that is manufactured to ASTM F480-90 (1992) standardcoupling.

DiameterChoice of casing diameter is also site-specific. Small wells are considered to be from 2 to 4 inches indiameter. The minimum diameter for use in monitoring wells is 2 inches. Advantages of small diameterwells are as follows:• Water levels require less time to recover after purging.• They produce a smaller volume of purged water that must be disposed.• Construction costs are lower.

Some disadvantages of small diameter wells include:• Access may be limited for sampling devices.• Filter packs and seals are more difficult to install.• They offer a lower depth capability due to lesser wall thickness.• Development can be more difficult.• Less ground water is pumped during a hydraulic test or a remediation extraction.• The amount of available water may be too small for chemical analyses.

Further discussion of well diameter can be found in articles by Schalla and Oberlander (1983), Schmidt(1982), and Rinaldo-Lee (1983).

75

InstallationCasing should be cleaned thoroughly before installation. Strong detergents and even steam cleaning

may be necessary to remove oils, cleansing solvents, lubricants, waxes, and other substances. (Curran andTomson, 1983; Barcelona et al., 1983). It is strongly recommended that only factory-cleaned materials beused for monitoring wells. Casing can be certified by the supplier and individually wrapped sections toretain cleanliness. If it has not been factory-cleaned and sealed, it should be washed thoroughly with anon-phosphate, laboratory grade detergent (e.g., Liquinox) and rinsed with clean water or distilled/deionized water as suggested by Curran and Tomson (1983) and Barcelona et al. (1983). The materialsshould be stored in a clean, protected place to prevent contamination by drilling and site activities.

When installing casing, it is important that it remain centered in the borehole to ensure proper place-ment and even distribution of the filter pack and annular seal. In addition, centering helps ensurestraightness for sampling device access. If a hollow-stem auger is used, no additional measures are neces-sary because the auger acts as a centralizing device. If casing is installed in an open borehole, centralizersmade of stainless steel or PVC can be used. They are adjustable and generally attached just above thescreen and at 10 to 20 foot intervals along the riser. If centralizers are used, measures should be taken toprevent them from bridging the filter pack and seal material during their installation.

IntakesAlthough every well is unique, most have a screen and filter pack. Together, these comprise an “intake”

Monitoring wells in cohesive bedrock may incorporate open borehole intakes.

Filter PackWells monitoring unconsolidated and some poorly consolidated materials typically need to have a

screen (discussed later) surrounded by more hydraulically conductive material (filter pack). In essence, thefilter pack increases the effective well diameter and prevents fine-grained material from entering.

Types of Filter PacksFilter packs can be classified by two major categories, natural and artificial. Natural packs are

created by allowing the formation to collapse around the screen. In general, natural packs arerecommended for formations that are coarse-grained, permeable, and uniform in grain size.According to Nielsen and Schalla (1991), they may be suitable when the effective grain size(sieve size that retains 90%, or passes 10%) is greater than 0.010 inch and the uniformity coeffi-cient (the ratio of the sieve size that retains 40% and the size that retains 90%) is greater than 3.Ideally, all fine-grained particles are removed when the well is developed, leaving the natural packas a filter to the surrounding formation.

Installation of artificial packs involves the direct placement of coarser-grained material aroundthe screen. The presence of this filter allows the use of a larger slot size than if the screen wereplaced in direct contact with the formation. Artificial packs generally are necessary where: 1) theformation is poorly sorted; 2) the intake spans several formations and/or thin, highly stratifiedmaterials with diverse grain sizes; 3) the formation is a uniform fine sand, silt or clay; 4) theformation consists of thinly-bedded materials, poorly cemented sandstones, and highly weathered,fractured, and solution-channeled bedrock; 5) shales and coals that provide a constant source ofturbidity are monitored; and 6) the borehole diameter is significantly greater than the diameter ofthe screen (Aller et al., 1991). Artificial packs generally are used opposite unconsolidated materi-als when the effective grain size is less than 0.010 inches and when the uniformity coefficient isless than 3.0 (Nielsen and Schalla, 1991).

An artificial pack may include two components. The primary pack extends from the bottom ofthe borehole to above the top of the screen. In some cases, it may be desirable to place a second-ary pack directly on top of the primary pack. Its purpose is to prevent the infiltration of theannular seal into the primary pack, which can partially or totally seal the screen.

Nature of Artificial Filter Pack MaterialThe artificial pack material should be well-sorted, well-rounded, clean, chemically inert, of

known origin, and free of all fine-grained clays, particles and organic material. Barcelona et al.(1983) recommended clean quartz sand or glass beads. Quartz is the best natural material due toits non-reactive properties and availability. Crushed limestone should never be used because of the

76

irregular particle size and potential chemical effects. Materials should be washed, dried, andpackaged at the factory, and typically are available in 100 lb. bags (approximately one cubic footof material) (Nielsen and Schalla, 1991).

Selection of material should be based on the formation particle size. If chosen grains are toosmall, it is possible that loss of the pack to the formation can occur (Nielsen and Schalla, 1991),which could lead to the settling of the annular seal into the screened interval. On the other hand, ifthe grains are too large, the pack will not effectively filter fine-grained material, leading toexcessively turbid samples.

The primary pack generally should range in grain size from a medium sand to a cobbledgravel. Most materials are available in ranges, such as 20- to 40-mesh (0.033 to 0.016 inches,Table 1). The grain size of the primary filter pack should be determined by multiplying the 70%retention size of the formation by a factor of 3 to 6 (U.S. EPA, 1975). A factor of 3 is used forfine, uniform formations; a factor of 6 is used for coarse, nonuniform formations (Figure 2). Insituations where the material is less uniform and the uniformity coefficient ranges from 6 to 10, itmay be necessary to use the 90% retention (10% passing) size multiplied by 6 (Nielsen andSchalla, 1991). This is to ensure that the bulk of the formation will be retained. The ratio of theparticle size to the formation grain size should not exceed 6, otherwise, the pack will becomeclogged with fine-grained material from the formation (Lehr et al., 1988). If the ratio is less than4, a smaller screen slot size will be necessary, full development of the well may not be possible,and well yield may be inhibited. When monitoring in very heterogeneous, layered stratigraphy, atype of pack should be chosen that suits the layer with the smallest grain size.

It is preferred that the filter pack be of uniform grain size. Ideally, the uniformity coefficientshould be as close to 1.0 as possible and should not exceed 2.5 (Nielsen and Schalla, 1991, ASTMD5092-90, 1994). Uniform material is much easier to install. If nonuniform material is used,differing fall velocities cause the materials to grade from coarse to fine upwards along the screen.This can result in the loss of the upper fine-grained portion to the well during development.

The secondary filter pack material should consist of a 90% retention sieve size (10% passing)that is larger than the voids of the primary pack to prevent the secondary pack from entering theprimary pack (Nielsen and Schalla, 1991). In general, the secondary 90% retention size should beone-third to one-fifth of the primary 90% retention size (Nielsen and Schalla, 1991).

Dimension of Artificial Filter PackThe distance between the casing and the borehole wall should be at least 2 to 4 inches to allow

for proper placement of the filter pack and annular seal. Therefore, the filter pack thickness shouldbe 2 to 4 inches. It is important that the thickness not be excessive, otherwise the potential foreffective development is reduced.

The primary pack should extend from the bottom of the screen to at least 2 feet above its top.In deeper wells (i.e., >200 feet), the pack may not compress initially. Compression may occur

Size of screen Slot No Sand Pack 1% Passing Effective Size 30% Passing Range of Roundness FallOPening Mesh Size Size (D1) (D10) Size (D30) Uniformity (Powers Velocities*[mm (in.)] (mm) (mm) (mm) Coefficient Scale) (cm/s)

0.125(0.005) 5 40-140 0.09-0.12 0.14-0.17 0.17-0.21 1.3-2.0 2-5 6-3

0.25 (0/010) 10 20-40 0.25-0.35 0.4-0.5 0.5-0.6 1.1-1.6 3-5 6-6

0.50 (0.020) 20 10-20 0.7-0.9 1.0-1.2 1.2-1.5 1.1-1.6 3-6 14-90.75 (0.030) 30 10-20 0.7-0.9 1.0-1.2 1.2-1.5 1.1-1.6 3-6 14-9

1.0 (0.040) 40 8-12 1.2-1.4 1.6-1.8 1.7-2.0 1.1-1.6 4-6 16-13

1.5 (0.060) 60 6-9 1.5-1.8 2.3-2.8 2.5-3.0 1.1-1.7 4-6 18-152.0 (0.080) 80 4-8 2.0-2.4 2.4-3.0 2.6-3.1 1.1-1.7 4-6 22-16

Table 1. Common filter pack characteristics for typical screen slot sizes. (From Nielsen and Schalla, 1991)

* Fall velocities in centimeters per second are approximate for the range of sand pack mesh sizes named in thistable. If water in the annular space is very turbid, fall velocities may be less than half the values shown here. If aviscous drilling mud remains in the annulus, fine particles may require hours to settle.

77

after installation of the annular seal, which may allow the seal to be in close contact with thescreen. Therefore, additional pack material may be needed to account for settling and, at the sametime, provide adequate separation of the seal and the screen. However, extension of the packshould not be excessive because it enlarges the zone that contributes ground water to the well,which may cause excess dilution. The length of the secondary pack should be one-foot or less.

Artificial Filter Pack InstallationMethods that have been used for artificial pack installation include tremie pipe, gravity em-

placement, reverse circulation, and backwashing (Nielsen and Schalla, 1991). The material mustbe placed in a manner that prevents bridging and particle segregation. Bridging can cause thepresence of large voids and may prevent material from reaching the intended depth. Segregationcan cause a well to produce turbid samples. During installation, regular measurements with aweighted tape should be conducted to determine when the desired height has been reached, andalso act as a tamping device to reduce bridging. The anticipated volume of filter pack should becalculated.4 Any discrepancy between the actual and calculated volumes should be explained.

The preferred method for artificial pack installation is to use a tremie pipe to emplace materialdirectly around the screen. The pipe is raised periodically to help minimize the risk of bridging.The pipe generally should be at least 1.5 inches ID, but larger diameters may be necessary wherecoarser-grained packs are being installed. When driven casing or hollow-stem augering is used topenetrate non-cohesive formations, the material should be tremied as the casing and auger ispulled back in one to two foot increments to reduce caving effects and ensure proper placement(Nielsen and Schalla, 1991). When installing wells through cohesive formations, the tremie pipecan be used after removal of the drilling device.

Gravity emplacement is accomplished by allowing material to free-fall to the desired positionaround the screen. Placement by gravity should be restricted to shallow wells with an annularspace greater than 2 inches, where the potential for bridging or segregation is minimized (Nielsenand Schalla, 1991). For low-yielding formations, it may be possible to bail the borehole dry tofacilitate placement; however, segregation is generally only a problem for deep wells with shallowwater levels. Also, segregation is generally not a problem if the pack has a uniformity coefficientof 2.5 or less. Gravity placement also can cause grading if the material is not uniform. In addition,

4 Anticipated filter pack volume can be calculated by determining the difference in volume between the borehole and casing(using outside diameter of the well) from the bottom of the borehole to the appropriate height above the well screen.

Figure 2. Artificial filter pack design criteria (Source: Design and Installation of Ground Water Monitoring Wellsby D.M. Nielsen and R. Schalla, Practical Handbook of Ground Water Monitoring, edited by DavidM. Nielsen, Copyright 1991 by Lewis Publishers, an imprint of CRC Press, Boca Raton, Florida.With permission.)

D1

D10

D30

D30 of Filter Pack is 5times Formation D30 Size

(e.g. 20-40 U.S.Sieve Size Filter Pack)

(e.g. Formation)

A proper filter pack materialis chosen from 3 to 6 multiplicationof the D 30 size of theformation material curve.

}

4

100

90

80

70

60

50

40

30

20

10

0

0

10

20

30

40

50

60

70

80

90

1000 10 20 30 40 50 60 70 80 90

100 50 40 30 20 16 12 8

Slot Opening and Grain Size, in Thousandths of an Inch.

Cum

ulat

ive

Per

cent

Ret

aine

d

Cum

ulat

ive

Per

cent

Pas

sing

U.S. Standard Sieve Numbers

100 120110

78

formation materials are often incorporated during placement, which can contaminate the pack andreduce its effectiveness. For most cases, gravity placement is not recommended.

Reverse circulation involves the insertion of a sand and water mixture through the annulus.Sand is deposited around the screen as the water returns to the surface through the casing. Due tothe potential water quality alteration, this method generally is not recommended.

Backwashing is accomplished by allowing material to free-fall through the annulus while cleanwater is pumped down the casing. The water returns up the annulus carrying fine-grained materialwith it. This creates a more uniform pack; however, the method is not commonly used for moni-toring well installation and generally is not recommended due to the potential for alteration ofground water quality. Nonetheless, it is sometimes used for placing packs opposite non-cohesiveheaving sands and silts.

ScreenThe screen is the final link to retaining the borehole and keeping unwanted formation particles out of

ground water samples.

Screen TypesRecommended screen compositions are stainless steel, PTFE, and PVC. The same discussion

and concerns for casing material apply to screens. Only manufactured screens should be used,since these are available with slots sized precisely for specific grain sizes. Field-cut or puncturedscreen should never be used, due to the inability to produce the necessary slot size and the poten-tial for the fresh surface to leach or sorb contaminants. A bottom cap or plug should be placed atthe base of the screen to prevent sediments from entering and to ensure that all water enters thewell through the screen openings.

Slotted and continuous slot, wire-wound screen are the common types used for monitoringwells. In deep wells, slotted screen generally retains structural integrity better than wire-wound;however, continuous slot, wire-wound screens provide almost twice the open area of slottedcasing. More open area per unit length enhances well recovery and development. A slot typeshould be chosen that provides the maximum amount of open area in relation to the effectiveporosity of the formation. Driscoll (1986) recommended that the percentage of open area shouldbe at least equal to the effective porosity of the formation and filter pack. In common situationswith 10 to 30 percent effective porosities, continuous slot screens are preferred, although notrequired (Nielsen and Schalla, 1991).

Slot SizeWhen selecting a screen slot size for an artificially filter-packed well, a sieve analysis should

be conducted on the pack material. The selected size should retain at least 90% of the pack. Inmany situations it is preferable to retain 99% (Nielsen and Schalla, 1991 and ASTM D 5092-90,1994) (Figure 3). See Table 1 for a guide to the selection of slot sizes for various packs.

For naturally-packed wells, the screen should retain from 30 to 60% (Aller et al., 1991). As arule of thumb, a 50% retention may be adequate (based on Wisconsin Administrative Code, 1990).With small diameter (4-inch or less), low yield wells, development may not be effective to removea sufficient amount of fines and a 60 to 70% retention size may be more desirable. For additionalinformation on pack and screen selection, see Aller et al. (1991), Nielsen and Schalla, (1991), andASTM D 5092-90 (1994).

It should be noted that if a PTFE screen is used in a deep well, a slightly larger slot size thanpredicted should be selected due to the material’s lower compressive strength, which allows theopenings to compress (Dablow et al., 1988).

LengthScreen length should be tailored to the desired zone and generally should not exceed 10 ft. A 2

to 5 ft. screen is desirable for more accurate sampling and discrete head measurements. Longerscreens produce composite samples that may be diluted by uncontaminated water. As a result,concentrations of contaminants may be underestimated. Furthermore, the screen should not extendthrough more than one water-bearing zone to avoid cross-contamination. When a thick formationmust be monitored, a cluster of individual, closely spaced wells, screened at various depths, can

79

be installed to monitor the entire formation thickness. The length of screens that monitor the watertable surface should account for seasonal fluctuation of the water table.

Open Borehole IntakesWhen constructing monitoring wells in competent bedrock, an artificial intake is often unnec-

essary because an open hole can be maintained and sediment movement is limited. Installing afilter pack in these situations may be difficult due to loss of material into the surrounding forma-tion. In some cases, however, intakes are a necessary component of bedrock wells. A screen andfilter pack should be installed in highly weathered, poorly cemented, and fractured bedrock(Nielsen and Schalla, 1991). They are usually necessary when monitoring the unconsolidated/consolidated interface in Ohio.

Open hole wells often are completed by casing and grouting the annulus prior to drilling intothe monitoring zone. In cases where the zone has been drilled prior to sealing the annulus, abridge (cement basket or formation packer shoe) must be set in the hole to retain the grout/slurryto the desired depth (Driscoll, 1986).

If an open hole well is installed, the length of open hole generally should not exceed 10 feet toprevent sample dilution. To maintain a discrete monitoring zone in consolidated formations, thecasing should be extended and grouted to the appropriate depth to maintain the 10 foot limit.Driven casing may be necessary to avoid loss of the annular seal into the surrounding formation.

Annular SealsThe open, annular space between the borehole wall and the casing must be sealed properly to: 1)

isolate a discrete zone, 2) prevent migration of surface water, 3) prevent vertical migration of groundwater between strata, and 4) preserve confining conditions by preventing the upward migration of wateralong the casing. An effective seal requires that the annulus be filled completely with sealant and thephysical integrity of the seal be maintained throughout the lifetime of the well (Aller et al., 1991).

Figure 3. Selection of screen slot size based on the filter pack grain size. (Source: Design and Installation ofGround Water Monitoring Wells by D.M. Nielsen and R. Schalla, Practical Handbook of GroundWater Monitoring, edited by David M. Nielsen, Copyright 1991 by Lewis Publishers, an imprint ofCRC Press, Boca Raton, Florida. With permission.)

D1

D10

D30

D30 of Filter Pack is 5times Formation D30 Size

(e.g. 20-40 U.S.Sieve Size Filter Pack)

(e.g. Formation)

A proper filter pack materialis chosen from 3 to 6 multiplicationof the D 30 size of theformation material curve.

}

4

100

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0

0

10

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100 50 40 30 20 16 12 8

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Cum

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Per

cent

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cent

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U.S. Standard Sieve Numbers

100 120110

80

MaterialsThe sealant must be of very low permeability (generally 10-7 to 10-9 cm/sec), capable of

bonding with casing, and chemically inert with the highest anticipated concentration of chemicalsexpected. Cuttings from the existing borehole, no matter what the type of materials, should neverbe used. They generally exhibit higher permeability and cannot form an adequate seal.

The most common materials used are bentonite and neat cement grout. Each has specific,unique, and desirable properties. These materials are discussed briefly here. Additional informa-tion can be found in Gaber and Fisher (1988), ASTM Method C-150 (1992), and Nielsen andSchalla (1991).

Neat Cement GroutNeat cement grout is comprised of portland cement and water, with no aggregates added. It is

a hydraulic cement produced by pulverizing cement clinker consisting essentially of hydratedcalcium silicates, and usually containing one or more forms of calcium sulfate as an intergroundaddition. Several types of portland cements are manufactured to accommodate various conditionsthat may be encountered. Table 2 lists the types as classified by ASTM C150-92 (1992). Type I ismost commonly used for monitoring wells.

Air-entraining portland cements have been specially processed to form minute air bubbleswithin the hardened structure. The air-entraining materials are added during the grinding of theclinker. The finished product is more resistant to freeze-thaw action. Air-entraining cements aredesignated with an “A” after the ASTM cement type. They have been used to construct watersupply wells; however, they are less desirable than standard cements because of their greaterpermeability. Therefore, air-entraining varieties are not recommended for subsurface sealing ofmonitoring wells.

Water added to the neat cement should be potable and contain less than 500 ppm total dis-solved solids (Gaber and Fisher, 1988). Low chloride and sulfate concentrations also are desir-able (Campbell and Lehr, 1973). As the water to cement ratio increases, the compressive strengthof the cement decreases and shrinkage increases. The American Petroleum Institute recommendsa ratio of 5.2 gallons of water per 94 pound sack of cement. Additional water makes it easier topump, but adversely affects the grout’s sealing properties. Excess water can cause shrinkage andseparation of the cement particles, which compromises seal integrity (Nielsen and Schalla, 1991).

The major disadvantages of neat cement are its heat of hydration, shrinkage upon curing, and itseffect on water quality. During curing, heat is released, which is generally of little concern; however,generally if large volumes of cement are used or the heat is not rapidly dissipated, the resulting high

General purpose cement suitable where special properties are not required.

Moderate sulfate resistance. Lower heat of hydration than Type I. Recommended for usewhere sulfate levels in ground water are between 150 to 1500 ppm.

High early strength. Ground to finer particle size, which increases surface area and providesfaster curing time period before drilling may resume from 48 hours to 12 hours. When TypeIII cement is used, the water-to-cement ratio must be increased to 6.3 to 7 gallons of waterper sack.

Low heat of hydration cement designated for applications where the rate and amount ofheat generated by the cement must be kept to a minimum. Develops strength at a lower ratethan Type I.

Sulfate-resistant cement for use where ground water has a high sulfate content. Recom-mended for use when levels in ground water exceed 1500 ppm.

Air entraining cements for the same use as Types I, II, and III. Not recommended for moni-toring well construction.

Type I

Type I

Type III

Type IV

Type V

Type IA, IIA,and IIIA

Table 2. ASTM Cement Designation (modified from Gaber and Fisher, 1988)

81

temperatures can compromise the integrity of PVC casing. However, the borehole for most monitoringwells is small, and heat significant enough to cause damage generally is not created.

Shrinkage is undesirable because it causes cracks and voids. To reduce cracking, 3 percentbentonite by weight can be added (Smith, 1994). Bentonite should not be pre-mixed with water,but should be added dry to the cement/water slurry (ASTM 5092-90, 1994). The addition ofbentonite also retards settling time and reduces peak temperatures. Other additives, such asaccelerators (e.g., calcium chloride) and retarders, are commercially available but are not recom-mended due to their potential to leach (ASTM Method 5092-90, 1994).

Upon settling, neat cement grouts often lose water into the formation and affect water quality.Neat cement typically ranges in pH from 10 to 12; therefore, it is important to isolate the annularseal from the screen and filter pack.

BentoniteBentonite is composed of clay particles that expand many times their original volume when

hydrated. The most acceptable form is a sodium (Na) rich montmorillonite clay that exhibits a 10to 12-fold expansion when hydrated. Other types, such as calcium (Ca) bentonite, are less desir-able because they offer lower swelling ability and surface area to mass ratios. However, othertypes should be considered if Na bentonite is incompatible with the formation or analyses ofconcern. For example, the capability of bentonite may be adversely affected by chloride salts,acids, alcohols, ketones, and other polar compounds. Ca bentonite may be more appropriate forcalcareous sediments.

Bentonite is available in a variety of forms, including pelletized, coarse grade, granular andpowder. Pellets are uniform in size and consist of compressed, powdered Na montmorillonite.They typically range from 1/4 to 1/2 inch in size. Pellets expand at a relatively slower rate whencompared to other forms. Coarse grade, also referred to as crushed or chipped, consists ofirregularly shaped, angular particles of montmorillonite that range from 1/4 to 3/4 inches in size.Granular particles range from 0.025 to 0.10 inches in size. Powdered bentonite is pulverizedmontmorillonite, factory-processed after mining. Powered and granular forms are generally mixedwith water to form a slurry. Risk of losing a slurry to the underlying filter pack and surroundingformation should be considered. High-solids, bentonite (>30% clay solids) has been developedspecifically for monitoring well construction and provides an effective seal.

Seal DesignIt is important that the design of annular seals prevent infiltration into the filter pack. Contact with the

seal can cause sampled ground water to be artificially high in pH. Additionally, bentonite has a high cationexchange capacity, which may affect the chemistry of samples (Aller et al., 1991). In the saturated zone, a2-foot pure bentonite seal can minimize the threat of infiltration. Above the bentonite seal, neat cement,bentonite, or neat cement/bentonite grouts should be placed in the remainder of the annulus to within afew feet of the surface. Because bentonite requires a sufficient quantity and quality of water in order toachieve and retain hydration, bentonite generally, should only be used in the saturated zone. Wheresaturated conditions do not exist, neat cement-bentonite should be used.

Seal InstallationIt is important that annular seals are installed using techniques that prevent bridging, which may cause

gaps, cracking or shrinking. Surface water and/or contaminants potentially can migrate through any voidscreated. The 2 foot bentonite seal above the filter pack is commonly installed by placing granular bento-nite, bentonite pellets, or bentonite chips around the casing by dropping them directly down the annulus. Iffeasible, this practice is acceptable for wells less than 30 feet deep if a tamping device is used. However,for wells deeper than 30 feet, coarse-grained bentonite should be placed by means of a tremie pipe.

The bentonite should be allowed to hydrate or cure prior to sealing the remainder of the annular space.This will help prevent invasion of grout into the screened interval. If a two foot bentonite seal is desired inthe unsaturated zone, granular material should be used. It should be added and hydrated in stages usingwater that is potable and free of analytes of concern.

For the remainder of the annulus, sealants should be in slurry form (e.g., cement grout, bentoniteslurry) and should be placed with a tremie pipe (Figure 4). The bottom of the pipe should be equippedwith a side discharge deflector to prevent the slurry from jetting a hole through the filter pack5. The seal

5 Side discharge deflectors may not be necessary when a bentonite seal has been placed properly.

82

should be allowed to completely hydrate,set, or cure in conformance with themanufacturer’s specifications prior tocompleting the surface seal and developingthe well.

Surface Seal/Protective CasingCompletions

Surface SealA neat cement or concrete

surface seal should be placedaround a protective casing to adepth just below the frost line (3-5ft.). If the same material was used inthe annular seal, the surface seal canbe a continuation; otherwise, thesurface seal is installed directly overthe annular seal after settling andcuring. The surface seal shouldslope away from the well andextend beyond the edge of theborehole to divert surface water.Air-entraining cements may bedesirable in cold climates to allevi-ate cracking caused by freezing andthawing.

Above-Ground CompletionsWhenever possible, monitoring

wells should extend above theground surface to prevent surfacewater from entering and to enhancevisibility. From the frost lineupward, a steel protective casingshould encompass the well. Theprotective casing should be at leasttwo inches larger in diameter than the inner casing, extend above it, and have a locking cap. Thelock should be protected by plastic or rubber covers so the use of lubricants to free and maintainlocking mechanisms can be avoided. A small drain or “weep hole” should be located just abovethe surface seal to prevent the accumulation of water between the casings (See Figure 1). This isespecially useful in cold climates, where the freezing of trapped water can damage the innercasing. A permanent reference point on the well inner casing must be surveyed to the nearest 0.01ft. This permanent marker should be used for all water level measurements. Additionally, the wellidentification number or code should be marked permanently and clearly.

Bumper or barrier guards should be placed beyond the edge of the surface seal or within 3 to 4feet of the well (See Figure 1). These guards are necessary to reduce and prevent accidentaldamage from vehicles. Painting the guard posts yellow or orange and installing reflectors canincrease visibility and help prevent mishaps.

Flush-to-Ground CompletionsFlush-to-ground completions are discouraged because the design increases the potential for

surface water infiltration; however, they are occasionally unavoidable. This type of completionshould be used only when the location of a well would disrupt traffic areas such as streets, parkinglots, and gas stations, or where easements require them (Nielsen and Schalla, 1991).

If flush-to-ground completion is installed, very careful procedures must be followed. A highlysecure subsurface vault generally is completed in the surface seal, allowing the well casing to be

Figure 4. Tremie pipe emplacement of annular seal material.(Source: Design and Installation of Ground WaterMonitoring Wells by D.M. Nielsen and R. Schalla,Practical Handbook of Ground Water Monitoring,edited by David M. Nielsen, Copyright 1991 byLewis Publishers Division, an imprint of CRCPress, Boca Raton, Florida. With permission.)

Water table

Groundsurface

Sand

Well intake/screen

Filter packmaterial (sand)

Funnel

Well casing

Borehole

Aquifer material

Sand

83

cut below grade (Figure 5). Anexpandable locking cap on thecasing and a waterproof gasketshould be installed around the vaultlid to prevent surface water infiltra-tion. The completion should beraised slightly above grade andsloped away to help divert surfacewater. It should be marked clearlyand locked to restrict access. Thisis especially important at gasstations to prevent themisidentification of wells asunderground tank filling points.

DocumentationDuring monitoring well installation,

pertinent information should be docu-mented, including design and construction,the drilling procedure, and the materialsencountered. Accurate “as-built” diagramsshould be prepared that, in general, includethe following:

• Date/time of start and comple-tion of construction.

• Boring/well number.• Drilling method and drilling

fluid used.• Borehole diameter and well

casing diameter.• Latitude and longitude.• Well location (+ 0.5 ft.) with

sketch of location.• Borehole depth (+ 0.1 ft.).• Well depth (+ 0.1 ft.).• Casing length and materials.• Screened interval(s).• Screen materials, length, design, and slot size.• Casing and screen joint type.• Depth/elevation of top and bottom of screen.• Filter pack material/size, volume calculations, and placement method.• Depth/elevation to top and bottom of filter pack.• Annular seal composition, volume (calculated and actual), and placement method.• Surface seal composition, placement method, and volume (calculated and actual).• Surface seal and well apron design/construction.• Depth/elevation of water.• Well development procedure and ground water turbidity.• Type/design of protective casing.• Well cap and lock.• Ground surface elevation (+ 0.01 ft.).• Surveyed reference point (+ 0.01 ft.) on well casing.• Detailed drawing of well (include dimensions).• Point where water encountered.• Water level after completion of well development.

Gasket

Annular Seal(cement/bentonite

or bentonite)

Borehole

Well casing

Vault lid

Vault

Well cap

Surface seal(Neat cementor concrete)

Figure 5. Typical flush-to-ground monitoring well completion.(Source: Design and Installation of Ground WaterMonitoring Wells by D.M. Nielsen and R. Schalla,Practical Handbook of Ground Water Monitoring,edited by David M. Nielsen, Copyright 1991 byLewis Publishers Division, an imprint of CRCPress, Boca Raton, Florida. With permission.)

84

In addition, the following should be documented in work plans (when appropriate) and reports:• Selection and rationale materials for selection of casing and screen.• Selection and rationale for well diameter, screen length, and screen slot size.• Filter pack selection and emplacement.• Annular sealant selection and emplacement.• Security measures.• Locations and elevations of wells.• Well development.

A complete, ongoing history of each well should be maintained. This can include sample collectiondates, dates and procedures for development, water level elevation data, problems, repairs, personnel, andmethods of decommissioning. This information should be kept as a permanent on-site file, available foragency review upon request.

On July 18, 1990, Ohio House Bill 476 went into effect. This bill requires that all logs for monitoringwells drilled in Ohio be submitted to the Ohio Department of Natural Resources, Division of Water(ODNR). The ODNR can be contacted for further information.

MaintenanceThe condition of wells must be maintained to keep them operational and insure that representative

samples can be obtained. Maintenance consists of conducting inspections and periodic checks on perfor-mance. Proper documentation (see previous section) is needed to serve as a benchmark for evaluation.Maintenance includes, but is not limited to, the following:

• Ensuring visibility and accessibility• Inspecting locks for rusting• Inspecting surface seals for cracking.• Checking survey marks to insure visibility.• Determining depth.• Removing sediments (if needed).• Evaluating performance by doing hydraulic conductivity tests.• Evaluating turbidity and redeveloping or replacing well if turbidity increases.

Routine inspections generally can be conducted during sampling. Additional evaluation can be con-ducted by comparing new ground water quality data with previous data. If the maintenance check indi-cates a problem, rehabilitation should be conducted.

85

Appendix VIIContact Agencies

Ohio Department of Agriculture (ODA), Pesticide Regulation SectionThe Ohio Department of Agriculture does not currently provide routine well analysis for

pesticides; however, the Pesticide Regulation Section of ODA will sample any well where it issuspected that the use of a pesticide may have contaminated the well. To protect sample integrity,they must be collected by an ODA inspector. Samples are then analyzed at the ODA laboratory inReynoldsburg. If a water sample is positive for a pesticide, the Pesticide Regulation Section willinvestigate to determine how the well was contaminated. The ODA will advise the well owner onhow to clean up the well, and, if necessary, take appropriate enforcement action under OhioPesticide Law. The Ohio Department of Agriculture can be contacted at 614-728-6200.

Ohio Department of Commerce, Division of State Fire Marshal, Bureau of Underground StorageTank Regulations (BUSTR)

In the event that any potable or non-potable water well is suspected of being contaminatedwith petroleum from a leaking petroleum underground storage tank (such as those used at gasstations), contact BUSTR at 1-800-686-2878.

Ohio Department of Health, Division of Quality AssuranceFor questions about possible contamination with substances other than pesticides or petroleum

products, contact the local health department or the Ohio Department of Health Private, WaterSystem Program (PWSP) at 614-466-1390.

To determine the registration status of a particular private water system contractor (i.e., drillingcontractor or pump installer), contact the local health department or the ODH-PWSP PublicInquiries Assistant at 614-466-0148.

Ohio Department of Natural Resources, Division of Mines and Reclamation*The Division of Mines and Reclamation regulates the abandonment of test borings for coal and

industrial minerals exploration through the permitting process under the Ohio Revised CodeChapter 1513 and 1514. Most exploratory borings are mined through the removal of the coal orindustrial mineral. Those borings that are not removed by mining are required to be properlysealed using procedures approved by the Division. The Division also recommends that the coaloperator properly seal any original private water supply wells that are replaced by a new welldrilled as a result of a water supply replacement order by the Chief. The Division investigates anyground water contamination complaints related to coal and industrial minerals mining activities.

Ohio Department of Natural Resources, Division of Oil & Gas*Personnel in the Ground water Protection section of the Division investigate ground water

contamination cases when oil and gas operations are the suspected cause. If there is reason tobelieve that an unsealed, unused well on a property is an oil or gas well, the Division also has anIdle and Orphan Well Program that addresses the need to seal abandoned oil and gas wells. Formore information on these two programs, contact the Division’s Central Office at 614-265-6926.

Ohio Department of Natural Resources, Division of WaterThe Ohio Revised Code, Section 1521.05, requires that well log and drilling reports be filed by

drilling contractors for wells drilled in the state. Well sealing reports also must be filed with theDivision of Water for any type of well sealed in Ohio. Again, this authority comes from Section1521.05 of the Ohio Revised Code. Requests for copies of well log and drilling reports and wellsealing reports on file can be made by calling 614-265-6740. Well log and drilling report formsand well sealing report forms can be obtained from the Division by calling 614-265-6739.

*Note: The Division of Mines and Reclamation and the Division of Oil and Gas have recently been combined to create the Division of Mineral Resources Management.

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Ohio Environmental Protection AgencyThe Ohio Revised Code 6111.42 gives the Ohio EPA authority to prescribe regulations for the

drilling, operation, maintenance, and sealing of abandoned wells as deemed necessary by thedirector to prevent the contamination of underground waters in the state, except that such regula-tions do not apply to non-public potable wells. For information on specific regulatory require-ments for public drinking water wells or for injection wells, the Division of Drinking and GroundWaters should be contacted at 614-644-2752.

The Ohio EPA has no regulations/requirements for a person to report contamination in theirprivate well. Reporting of ground water contamination is only required if an entity is monitoringground water in accordance with hazardous or solid waste rules. In general, the Ohio EPA will notrespond to a request to evaluate a contaminated private well unless the local or state healthdepartment requests assistance in investigating the source of the problem. However, this will notaffect how the well should be sealed, but may affect when it is sealed if additional investigation isinitiated.

An exception to this occurs if the well was used to inject fluid waste. If it was used as aninjection well, the owner/operator must contact the Division of Drinking and Ground Waters,Underground Injection Control Unit (U.I.C.) of the Ohio EPA at 614-644-2905. Specific require-ments must be followed for the sealing of injection wells.

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Documents

Cover Well Construction Guide